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Let's convert it like we converted all the other rmap functions. Don't
introduce folio_try_share_anon_rmap_ptes() for now, as we don't have a
user that wants rmap batching in sight. Pretty easy to add later.
All users are easy to convert -- only ksm.c doesn't use folios yet but
that is left for future work -- so let's just do it in a single shot.
While at it, turn the BUG_ON into a WARN_ON_ONCE.
Note that page_try_share_anon_rmap() so far didn't care about pte/pmd
mappings (no compound parameter). We're changing that so we can perform
better sanity checks and make the code actually more readable/consistent.
For example, __folio_rmap_sanity_checks() will make sure that a PMD range
actually falls completely into the folio.
Link: https://lkml.kernel.org/r/20231220224504.646757-39-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's get rid of the compound parameter and instead define explicitly
which mappings we're adding. That is more future proof, easier to read
and harder to mess up.
Use an enum to express the granularity internally. Make the compiler
always special-case on the granularity by using __always_inline. Replace
the "compound" check by a switch-case that will be removed by the compiler
completely.
Add plenty of sanity checks with CONFIG_DEBUG_VM. Replace the
folio_test_pmd_mappable() check by a config check in the caller and sanity
checks. Convert the single user of folio_add_file_rmap_range().
While at it, consistently use "int" instead of "unisgned int" in rmap code
when dealing with mapcounts and the number of pages.
This function design can later easily be extended to PUDs and to batch
PMDs. Note that for now we don't support anything bigger than PMD-sized
folios (as we cleanly separated hugetlb handling). Sanity checks will
catch if that ever changes.
Next up is removing page_remove_rmap() along with its "compound" parameter
and smilarly converting all other rmap functions.
Link: https://lkml.kernel.org/r/20231220224504.646757-8-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
hugetlb rmap handling differs quite a lot from "ordinary" rmap code. For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE". Let's move it out of the
way so we can overhaul our "ordinary" rmap. implementation/interface.
So let's introduce and use hugetlb_try_dup_anon_rmap() to make all hugetlb
handling use dedicated hugetlb_* rmap functions.
Add sanity checks that we end up with the right folios in the right
functions.
Note that try_to_unmap_one() does not need care. Easy to spot because
among all that nasty hugetlb special-casing in that function, we're not
using set_huge_pte_at() on the anon path -- well, and that code assumes
that we would want to swapout.
Link: https://lkml.kernel.org/r/20231220224504.646757-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
hugetlb rmap handling differs quite a lot from "ordinary" rmap code. For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE". Let's move it out of the
way so we can overhaul our "ordinary" rmap. implementation/interface.
Right now we're using page_dup_file_rmap() in some cases where "ordinary"
rmap code would have used page_add_file_rmap(). So let's introduce and
use hugetlb_add_file_rmap() instead. We won't be adding a
"hugetlb_dup_file_rmap()" functon for the fork() case, as it would be
doing the same: "dup" is just an optimization for "add".
What remains is a single page_dup_file_rmap() call in fork() code.
Add sanity checks that we end up with the right folios in the right
functions.
Link: https://lkml.kernel.org/r/20231220224504.646757-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
hugetlb rmap handling differs quite a lot from "ordinary" rmap code. For
example, hugetlb currently only supports entire mappings, and treats any
mapping as mapped using a single "logical PTE". Let's move it out of the
way so we can overhaul our "ordinary" rmap. implementation/interface.
Let's introduce and use hugetlb_remove_rmap() and remove the hugetlb code
from page_remove_rmap(). This effectively removes one check on the
small-folio path as well.
Add sanity checks that we end up with the right folios in the right
functions.
Note: all possible candidates that need care are page_remove_rmap() that
pass compound=true.
Link: https://lkml.kernel.org/r/20231220224504.646757-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/rmap: interface overhaul", v2.
This series overhauls the rmap interface, to get rid of the "bool
compound" / RMAP_COMPOUND parameter with the goal of making the interface
less error prone, more future proof, and more natural to extend to
"batching". Also, this converts the interface to always consume
folio+subpage, which speeds up operations on large folios.
Further, this series adds PTE-batching variants for 4 rmap functions,
whereby only folio_add_anon_rmap_ptes() is used for batching in this
series when PTE-remapping a PMD-mapped THP. folio_remove_rmap_ptes(),
folio_try_dup_anon_rmap_ptes() and folio_dup_file_rmap_ptes() will soon
come in handy[1,2].
This series performs a lot of folio conversion along the way. Most of the
added LOC in the diff are only due to documentation.
As we're moving to a pte/pmd interface where we clearly express the
mapping granularity we are dealing with, we first get the remainder of
hugetlb out of the way, as it is special and expected to remain special:
it treats everything as a "single logical PTE" and only currently allows
entire mappings.
Even if we'd ever support partial mappings, I strongly assume the
interface and implementation will still differ heavily: hopefull we can
avoid working on subpages/subpage mapcounts completely and only add a
"count" parameter for them to enable batching.
New (extended) hugetlb interface that operates on entire folio:
* hugetlb_add_new_anon_rmap() -> Already existed
* hugetlb_add_anon_rmap() -> Already existed
* hugetlb_try_dup_anon_rmap()
* hugetlb_try_share_anon_rmap()
* hugetlb_add_file_rmap()
* hugetlb_remove_rmap()
New "ordinary" interface for small folios / THP::
* folio_add_new_anon_rmap() -> Already existed
* folio_add_anon_rmap_[pte|ptes|pmd]()
* folio_try_dup_anon_rmap_[pte|ptes|pmd]()
* folio_try_share_anon_rmap_[pte|pmd]()
* folio_add_file_rmap_[pte|ptes|pmd]()
* folio_dup_file_rmap_[pte|ptes|pmd]()
* folio_remove_rmap_[pte|ptes|pmd]()
folio_add_new_anon_rmap() will always map at the largest granularity
possible (currently, a single PMD to cover a PMD-sized THP). Could be
extended if ever required.
In the future, we might want "_pud" variants and eventually "_pmds"
variants for batching.
I ran some simple microbenchmarks on an Intel(R) Xeon(R) Silver 4210R:
measuring munmap(), fork(), cow, MADV_DONTNEED on each PTE ... and PTE
remapping PMD-mapped THPs on 1 GiB of memory.
For small folios, there is barely a change (< 1% improvement for me).
For PTE-mapped THP:
* PTE-remapping a PMD-mapped THP is more than 10% faster.
* fork() is more than 4% faster.
* MADV_DONTNEED is 2% faster
* COW when writing only a single byte on a COW-shared PTE is 1% faster
* munmap() barely changes (< 1%).
[1] https://lkml.kernel.org/r/20230810103332.3062143-1-ryan.roberts@arm.com
[2] https://lkml.kernel.org/r/20231204105440.61448-1-ryan.roberts@arm.com
This patch (of 40):
Let's just call it "hugetlb_".
Yes, it's all already inconsistent and confusing because we have a lot of
"hugepage_" functions for legacy reasons. But "hugetlb" cannot possibly
be confused with transparent huge pages, and it matches "hugetlb.c" and
"folio_test_hugetlb()". So let's minimize confusion in rmap code.
Link: https://lkml.kernel.org/r/20231220224504.646757-1-david@redhat.com
Link: https://lkml.kernel.org/r/20231220224504.646757-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Implement the uABI of UFFDIO_MOVE ioctl.
UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application
needs pages to be allocated [1]. However, with UFFDIO_MOVE, if pages are
available (in userspace) for recycling, as is usually the case in heap
compaction algorithms, then we can avoid the page allocation and memcpy
(done by UFFDIO_COPY). Also, since the pages are recycled in the
userspace, we avoid the need to release (via madvise) the pages back to
the kernel [2].
We see over 40% reduction (on a Google pixel 6 device) in the compacting
thread's completion time by using UFFDIO_MOVE vs. UFFDIO_COPY. This was
measured using a benchmark that emulates a heap compaction implementation
using userfaultfd (to allow concurrent accesses by application threads).
More details of the usecase are explained in [2]. Furthermore,
UFFDIO_MOVE enables moving swapped-out pages without touching them within
the same vma. Today, it can only be done by mremap, however it forces
splitting the vma.
[1] https://lore.kernel.org/all/1425575884-2574-1-git-send-email-aarcange@redhat.com/
[2] https://lore.kernel.org/linux-mm/CA+EESO4uO84SSnBhArH4HvLNhaUQ5nZKNKXqxRCyjniNVjp0Aw@mail.gmail.com/
Update for the ioctl_userfaultfd(2) manpage:
UFFDIO_MOVE
(Since Linux xxx) Move a continuous memory chunk into the
userfault registered range and optionally wake up the blocked
thread. The source and destination addresses and the number of
bytes to move are specified by the src, dst, and len fields of
the uffdio_move structure pointed to by argp:
struct uffdio_move {
__u64 dst; /* Destination of move */
__u64 src; /* Source of move */
__u64 len; /* Number of bytes to move */
__u64 mode; /* Flags controlling behavior of move */
__s64 move; /* Number of bytes moved, or negated error */
};
The following value may be bitwise ORed in mode to change the
behavior of the UFFDIO_MOVE operation:
UFFDIO_MOVE_MODE_DONTWAKE
Do not wake up the thread that waits for page-fault
resolution
UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES
Allow holes in the source virtual range that is being moved.
When not specified, the holes will result in ENOENT error.
When specified, the holes will be accounted as successfully
moved memory. This is mostly useful to move hugepage aligned
virtual regions without knowing if there are transparent
hugepages in the regions or not, but preventing the risk of
having to split the hugepage during the operation.
The move field is used by the kernel to return the number of
bytes that was actually moved, or an error (a negated errno-
style value). If the value returned in move doesn't match the
value that was specified in len, the operation fails with the
error EAGAIN. The move field is output-only; it is not read by
the UFFDIO_MOVE operation.
The operation may fail for various reasons. Usually, remapping of
pages that are not exclusive to the given process fail; once KSM
might deduplicate pages or fork() COW-shares pages during fork()
with child processes, they are no longer exclusive. Further, the
kernel might only perform lightweight checks for detecting whether
the pages are exclusive, and return -EBUSY in case that check fails.
To make the operation more likely to succeed, KSM should be
disabled, fork() should be avoided or MADV_DONTFORK should be
configured for the source VMA before fork().
This ioctl(2) operation returns 0 on success. In this case, the
entire area was moved. On error, -1 is returned and errno is
set to indicate the error. Possible errors include:
EAGAIN The number of bytes moved (i.e., the value returned in
the move field) does not equal the value that was
specified in the len field.
EINVAL Either dst or len was not a multiple of the system page
size, or the range specified by src and len or dst and len
was invalid.
EINVAL An invalid bit was specified in the mode field.
ENOENT
The source virtual memory range has unmapped holes and
UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES is not set.
EEXIST
The destination virtual memory range is fully or partially
mapped.
EBUSY
The pages in the source virtual memory range are either
pinned or not exclusive to the process. The kernel might
only perform lightweight checks for detecting whether the
pages are exclusive. To make the operation more likely to
succeed, KSM should be disabled, fork() should be avoided
or MADV_DONTFORK should be configured for the source virtual
memory area before fork().
ENOMEM Allocating memory needed for the operation failed.
ESRCH
The target process has exited at the time of a UFFDIO_MOVE
operation.
Link: https://lkml.kernel.org/r/20231206103702.3873743-3-surenb@google.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "userfaultfd move option", v6.
This patch series introduces UFFDIO_MOVE feature to userfaultfd, which has
long been implemented and maintained by Andrea in his local tree [1], but
was not upstreamed due to lack of use cases where this approach would be
better than allocating a new page and copying the contents. Previous
upstraming attempts could be found at [6] and [7].
UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application
needs pages to be allocated [2]. However, with UFFDIO_MOVE, if pages are
available (in userspace) for recycling, as is usually the case in heap
compaction algorithms, then we can avoid the page allocation and memcpy
(done by UFFDIO_COPY). Also, since the pages are recycled in the
userspace, we avoid the need to release (via madvise) the pages back to
the kernel [3]. We see over 40% reduction (on a Google pixel 6 device) in
the compacting thread's completion time by using UFFDIO_MOVE vs.
UFFDIO_COPY. This was measured using a benchmark that emulates a heap
compaction implementation using userfaultfd (to allow concurrent accesses
by application threads). More details of the usecase are explained in
[3].
Furthermore, UFFDIO_MOVE enables moving swapped-out pages without
touching them within the same vma. Today, it can only be done by mremap,
however it forces splitting the vma.
TODOs for follow-up improvements:
- cross-mm support. Known differences from single-mm and missing pieces:
- memcg recharging (might need to isolate pages in the process)
- mm counters
- cross-mm deposit table moves
- cross-mm test
- document the address space where src and dest reside in struct
uffdio_move
- TLB flush batching. Will require extensive changes to PTL locking in
move_pages_pte(). OTOH that might let us reuse parts of mremap code.
This patch (of 5):
For now, folio_move_anon_rmap() was only used to move a folio to a
different anon_vma after fork(), whereby the root anon_vma stayed
unchanged. For that, it was sufficient to hold the folio lock when
calling folio_move_anon_rmap().
However, we want to make use of folio_move_anon_rmap() to move folios
between VMAs that have a different root anon_vma. As folio_referenced()
performs an RMAP walk without holding the folio lock but only holding the
anon_vma in read mode, holding the folio lock is insufficient.
When moving to an anon_vma with a different root anon_vma, we'll have to
hold both, the folio lock and the anon_vma lock in write mode.
Consequently, whenever we succeeded in folio_lock_anon_vma_read() to
read-lock the anon_vma, we have to re-check if the mapping was changed in
the meantime. If that was the case, we have to retry.
Note that folio_move_anon_rmap() must only be called if the anon page is
exclusive to a process, and must not be called on KSM folios.
This is a preparation for UFFDIO_MOVE, which will hold the folio lock, the
anon_vma lock in write mode, and the mmap_lock in read mode.
Link: https://lkml.kernel.org/r/20231206103702.3873743-1-surenb@google.com
Link: https://lkml.kernel.org/r/20231206103702.3873743-2-surenb@google.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: kernel-team@android.com
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Multi-size THP for anonymous memory", v9.
A series to implement multi-size THP (mTHP) for anonymous memory
(previously called "small-sized THP" and "large anonymous folios").
The objective of this is to improve performance by allocating larger
chunks of memory during anonymous page faults:
1) Since SW (the kernel) is dealing with larger chunks of memory than base
pages, there are efficiency savings to be had; fewer page faults, batched PTE
and RMAP manipulation, reduced lru list, etc. In short, we reduce kernel
overhead. This should benefit all architectures.
2) Since we are now mapping physically contiguous chunks of memory, we can take
advantage of HW TLB compression techniques. A reduction in TLB pressure
speeds up kernel and user space. arm64 systems have 2 mechanisms to coalesce
TLB entries; "the contiguous bit" (architectural) and HPA (uarch).
This version incorporates David's feedback on the core patches (#3, #4)
and adds some RB and TB tags (see change log for details).
By default, the existing behaviour (and performance) is maintained. The
user must explicitly enable multi-size THP to see the performance benefit.
This is done via a new sysfs interface (as recommended by David
Hildenbrand - thanks to David for the suggestion)! This interface is
inspired by the existing per-hugepage-size sysfs interface used by
hugetlb, provides full backwards compatibility with the existing PMD-size
THP interface, and provides a base for future extensibility. See [9] for
detailed discussion of the interface.
This series is based on mm-unstable (715b67adf4c8).
Prerequisites
=============
I'm removing this section on the basis that I don't believe what we were
previously calling prerequisites are really prerequisites anymore. We
originally defined them when mTHP was a compile-time feature. There is
now a runtime control to opt-in to mTHP; when disabled, correctness and
performance are as before. When enabled, the code is still
correct/robust, but in the absence of the one remaining item (compaction)
there may be a performance impact in some corners. See the old list in
the v8 cover letter at [8]. And a longer explanation of my thinking here
[10].
SUMMARY: I don't think we should hold this series up, waiting for the
items on the prerequisites list. I believe this series should be ready
now so hopefully can be added to mm-unstable for some testing, then
fingers crossed for v6.8.
Testing
=======
The series includes patches for mm selftests to enlighten the cow and
khugepaged tests to explicitly test with multi-size THP, in the same way
that PMD-sized THP is tested. The new tests all pass, and no regressions
are observed in the mm selftest suite. I've also run my usual kernel
compilation and java script benchmarks without any issues.
Refer to my performance numbers posted with v6 [6]. (These are for
multi-size THP only - they do not include the arm64 contpte follow-on
series).
John Hubbard at Nvidia has indicated dramatic 10x performance improvements
for some workloads at [11]. (Observed using v6 of this series as well as
the arm64 contpte series).
Kefeng Wang at Huawei has also indicated he sees improvements at [12] although
there are some latency regressions also.
I've also checked that there is no regression in the write fault path when
mTHP is disabled using a microbenchmark. I ran it for a baseline kernel,
as well as v8 and v9. I repeated on Ampere Altra (bare metal) and Apple
M2 (VM):
| | m2 vm | altra |
|--------------|---------------------|---------------------|
| kernel | mean | std_rel | mean | std_rel |
|--------------|----------|----------|----------|----------|
| baseline | 0.000% | 0.341% | 0.000% | 3.581% |
| anonfolio-v8 | 0.005% | 0.272% | 5.068% | 1.128% |
| anonfolio-v9 | -0.013% | 0.442% | 0.107% | 1.788% |
There is no measurable difference on M2, but altra has a slow down in v8
which is fixed in v9 by moving the THP order check to be inline within
thp_vma_allowable_orders(), as suggested by David.
This patch (of 10):
In preparation for the introduction of anonymous multi-size THP, we would
like to be able to split them when they have unmapped subpages, in order
to free those unused pages under memory pressure. So remove the
artificial requirement that the large folio needed to be at least
PMD-sized.
Link: https://lkml.kernel.org/r/20231207161211.2374093-1-ryan.roberts@arm.com
Link: https://lkml.kernel.org/r/20231207161211.2374093-2-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Barry Song <v-songbaohua@oppo.com>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: John Hubbard <jhubbard@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Itaru Kitayama <itaru.kitayama@gmail.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/rmap: convert page_move_anon_rmap() to
folio_move_anon_rmap()".
Convert page_move_anon_rmap() to folio_move_anon_rmap(), letting the
callers handle PageAnonExclusive. I'm including cleanup patch #3 because
it fits into the picture and can be done cleaner by the conversion.
This patch (of 3):
Let's move it into the caller: there is a difference between whether an
anon folio can only be mapped by one process (e.g., into one VMA), and
whether it is truly exclusive (e.g., no references -- including GUP --
from other processes).
Further, for large folios the page might not actually be pointing at the
head page of the folio, so it better be handled in the caller. This is a
preparation for converting page_move_anon_rmap() to consume a folio.
Link: https://lkml.kernel.org/r/20231002142949.235104-1-david@redhat.com
Link: https://lkml.kernel.org/r/20231002142949.235104-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
If large folio is in the range of VM_LOCKED VMA, it should be mlocked to
avoid being picked by page reclaim. Which may split the large folio and
then mlock each pages again.
Mlock this kind of large folio to prevent them being picked by page
reclaim.
For the large folio which cross the boundary of VM_LOCKED VMA or not fully
mapped to VM_LOCKED VMA, we'd better not to mlock it. So if the system is
under memory pressure, this kind of large folio will be split and the
pages ouf of VM_LOCKED VMA can be reclaimed.
Ideally, for large folio, we should mlock it when the large folio is fully
mapped to VMA and munlock it if any page are unmampped from VMA. But it's
not easy to detect whether the large folio is fully mapped to VMA in some
cases (like add/remove rmap). So we update mlock_vma_folio() and
munlock_vma_folio() to mlock/munlock the folio according to vma->vm_flags.
Let caller to decide whether they should call these two functions.
For add rmap, only mlock normal 4K folio and postpone large folio handling
to page reclaim phase. It is possible to reuse page table iterator to
detect whether folio is fully mapped or not during page reclaim phase.
For remove rmap, invoke munlock_vma_folio() to munlock folio unconditionly
because rmap makes folio not fully mapped to VMA.
Link: https://lkml.kernel.org/r/20230918073318.1181104-3-fengwei.yin@intel.com
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's handle it in the caller; no need for the "first" check based on the
mapcount.
We really only end up with !anon pages in page_add_anon_rmap() via
do_swap_page(), where we hold the folio lock. So races are not possible.
Add a VM_WARN_ON_FOLIO() to make sure that we really hold the folio lock.
In the future, we might want to let do_swap_page() use
folio_add_new_anon_rmap() on new pages instead: however, we might have to
pass then whether the folio is exclusive or not. So keep it in there for
now.
For hugetlb we never expect to have a non-anon page in
hugepage_add_anon_rmap(). Remove that code, along with some other checks
that are either not required or were checked in
hugepage_add_new_anon_rmap() already.
Link: https://lkml.kernel.org/r/20230913125113.313322-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Anon rmap cleanups".
Some cleanups around rmap for anon pages. I'm working on more cleanups
also around file rmap -- also to handle the "compound" parameter
internally only and to let hugetlb use page_add_file_rmap(), but these
changes make sense separately.
This patch (of 6):
That comment was added in commit 5dbe0af47f ("mm: fix kernel BUG at
mm/rmap.c:1017!") to document why we can see vma->vm_end getting adjusted
concurrently due to a VMA split.
However, the optimized locking code was changed again in bf181b9f9d ("mm
anon rmap: replace same_anon_vma linked list with an interval tree.").
... and later, the comment was changed in commit 0503ea8f5b ("mm/mmap:
remove __vma_adjust()") to talk about "vma_merge" although the original
issue was with VMA splitting.
Let's just remove that comment. Nowadays, it's outdated, imprecise and
confusing.
Link: https://lkml.kernel.org/r/20230913125113.313322-1-david@redhat.com
Link: https://lkml.kernel.org/r/20230913125113.313322-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "Fix set_huge_pte_at() panic on arm64", v2.
This series fixes a bug in arm64's implementation of set_huge_pte_at(),
which can result in an unprivileged user causing a kernel panic. The
problem was triggered when running the new uffd poison mm selftest for
HUGETLB memory. This test (and the uffd poison feature) was merged for
v6.5-rc7.
Ideally, I'd like to get this fix in for v6.6 and I've cc'ed stable
(correctly this time) to get it backported to v6.5, where the issue first
showed up.
Description of Bug
==================
arm64's huge pte implementation supports multiple huge page sizes, some of
which are implemented in the page table with multiple contiguous entries.
So set_huge_pte_at() needs to work out how big the logical pte is, so that
it can also work out how many physical ptes (or pmds) need to be written.
It previously did this by grabbing the folio out of the pte and querying
its size.
However, there are cases when the pte being set is actually a swap entry.
But this also used to work fine, because for huge ptes, we only ever saw
migration entries and hwpoison entries. And both of these types of swap
entries have a PFN embedded, so the code would grab that and everything
still worked out.
But over time, more calls to set_huge_pte_at() have been added that set
swap entry types that do not embed a PFN. And this causes the code to go
bang. The triggering case is for the uffd poison test, commit
99aa77215a ("selftests/mm: add uffd unit test for UFFDIO_POISON"), which
causes a PTE_MARKER_POISONED swap entry to be set, coutesey of commit
8a13897fb0 ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs") -
added in v6.5-rc7. Although review shows that there are other call sites
that set PTE_MARKER_UFFD_WP (which also has no PFN), these don't trigger
on arm64 because arm64 doesn't support UFFD WP.
If CONFIG_DEBUG_VM is enabled, we do at least get a BUG(), but otherwise,
it will dereference a bad pointer in page_folio():
static inline struct folio *hugetlb_swap_entry_to_folio(swp_entry_t entry)
{
VM_BUG_ON(!is_migration_entry(entry) && !is_hwpoison_entry(entry));
return page_folio(pfn_to_page(swp_offset_pfn(entry)));
}
Fix
===
The simplest fix would have been to revert the dodgy cleanup commit
18f3962953 ("mm: hugetlb: kill set_huge_swap_pte_at()"), but since
things have moved on, this would have required an audit of all the new
set_huge_pte_at() call sites to see if they should be converted to
set_huge_swap_pte_at(). As per the original intent of the change, it
would also leave us open to future bugs when people invariably get it
wrong and call the wrong helper.
So instead, I've added a huge page size parameter to set_huge_pte_at().
This means that the arm64 code has the size in all cases. It's a bigger
change, due to needing to touch the arches that implement the function,
but it is entirely mechanical, so in my view, low risk.
I've compile-tested all touched arches; arm64, parisc, powerpc, riscv,
s390, sparc (and additionally x86_64). I've additionally booted and run
mm selftests against arm64, where I observe the uffd poison test is fixed,
and there are no other regressions.
This patch (of 2):
In order to fix a bug, arm64 needs to be told the size of the huge page
for which the pte is being set in set_huge_pte_at(). Provide for this by
adding an `unsigned long sz` parameter to the function. This follows the
same pattern as huge_pte_clear().
This commit makes the required interface modifications to the core mm as
well as all arches that implement this function (arm64, parisc, powerpc,
riscv, s390, sparc). The actual arm64 bug will be fixed in a separate
commit.
No behavioral changes intended.
Link: https://lkml.kernel.org/r/20230922115804.2043771-1-ryan.roberts@arm.com
Link: https://lkml.kernel.org/r/20230922115804.2043771-2-ryan.roberts@arm.com
Fixes: 8a13897fb0 ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs")
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu> [powerpc 8xx]
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com> [vmalloc change]
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: <stable@vger.kernel.org> [6.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "arm64: support batched/deferred tlb shootdown during page
reclamation/migration", v11.
Though ARM64 has the hardware to do tlb shootdown, the hardware
broadcasting is not free. A simplest micro benchmark shows even on
snapdragon 888 with only 8 cores, the overhead for ptep_clear_flush is
huge even for paging out one page mapped by only one process: 5.36% a.out
[kernel.kallsyms] [k] ptep_clear_flush
While pages are mapped by multiple processes or HW has more CPUs, the cost
should become even higher due to the bad scalability of tlb shootdown.
The same benchmark can result in 16.99% CPU consumption on ARM64 server
with around 100 cores according to the test on patch 4/4.
This patchset leverages the existing BATCHED_UNMAP_TLB_FLUSH by
1. only send tlbi instructions in the first stage -
arch_tlbbatch_add_mm()
2. wait for the completion of tlbi by dsb while doing tlbbatch
sync in arch_tlbbatch_flush()
Testing on snapdragon shows the overhead of ptep_clear_flush is removed by
the patchset. The micro benchmark becomes 5% faster even for one page
mapped by single process on snapdragon 888.
Since BATCHED_UNMAP_TLB_FLUSH is implemented only on x86, the patchset
does some renaming/extension for the current implementation first (Patch
1-3), then add the support on arm64 (Patch 4).
This patch (of 4):
The entire scheme of deferred TLB flush in reclaim path rests on the fact
that the cost to refill TLB entries is less than flushing out individual
entries by sending IPI to remote CPUs. But architecture can have
different ways to evaluate that. Hence apart from checking
TTU_BATCH_FLUSH in the TTU flags, rest of the decision should be
architecture specific.
[yangyicong@hisilicon.com: rebase and fix incorrect return value type]
Link: https://lkml.kernel.org/r/20230717131004.12662-1-yangyicong@huawei.com
Link: https://lkml.kernel.org/r/20230717131004.12662-2-yangyicong@huawei.com
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
[https://lore.kernel.org/linuxppc-dev/20171101101735.2318-2-khandual@linux.vnet.ibm.com/]
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Tested-by: Punit Agrawal <punit.agrawal@bytedance.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Darren Hart <darren@os.amperecomputing.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: lipeifeng <lipeifeng@oppo.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Miao <realmz6@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Zeng Tao <prime.zeng@hisilicon.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Nadav Amit <namit@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The only instances of get_user_pages_remote() invocations which used the
vmas parameter were for a single page which can instead simply look up the
VMA directly. In particular:-
- __update_ref_ctr() looked up the VMA but did nothing with it so we simply
remove it.
- __access_remote_vm() was already using vma_lookup() when the original
lookup failed so by doing the lookup directly this also de-duplicates the
code.
We are able to perform these VMA operations as we already hold the
mmap_lock in order to be able to call get_user_pages_remote().
As part of this work we add get_user_page_vma_remote() which abstracts the
VMA lookup, error handling and decrementing the page reference count should
the VMA lookup fail.
This forms part of a broader set of patches intended to eliminate the vmas
parameter altogether.
[akpm@linux-foundation.org: avoid passing NULL to PTR_ERR]
Link: https://lkml.kernel.org/r/d20128c849ecdbf4dd01cc828fcec32127ed939a.1684350871.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> (for arm64)
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com> (for s390)
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Christian König <christian.koenig@amd.com>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Protect VMA from concurrent page fault handler while collapsing a huge
page. Page fault handler needs a stable PMD to use PTL and relies on
per-VMA lock to prevent concurrent PMD changes. pmdp_collapse_flush(),
set_huge_pmd() and collapse_and_free_pmd() can modify a PMD, which will
not be detected by a page fault handler without proper locking.
Before this patch, page tables can be walked under any one of the
mmap_lock, the mapping lock, and the anon_vma lock; so when khugepaged
unlinks and frees page tables, it must ensure that all of those either are
locked or don't exist. This patch adds a fourth lock under which page
tables can be traversed, and so khugepaged must also lock out that one.
[surenb@google.com: vm_lock/i_mmap_rwsem inversion in retract_page_tables]
Link: https://lkml.kernel.org/r/20230303213250.3555716-1-surenb@google.com
[surenb@google.com: build fix]
Link: https://lkml.kernel.org/r/CAJuCfpFjWhtzRE1X=J+_JjgJzNKhq-=JT8yTBSTHthwp0pqWZw@mail.gmail.com
Link: https://lkml.kernel.org/r/20230227173632.3292573-16-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old
in set_tlb_ubc_flush_pending. 86 CMPXCHG instruction returns success in
ZF flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails.
No functional change intended.
Link: https://lkml.kernel.org/r/20230227214228.3533299-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
After a memory error happens on a clean folio, a process unexpectedly
receives SIGBUS when it accesses the error page. This SIGBUS killing is
pointless and simply degrades the level of RAS of the system, because the
clean folio can be dropped without any data lost on memory error handling
as we do for a clean pagecache.
When memory_failure() is called on a clean folio, try_to_unmap() is called
twice (one from split_huge_page() and one from hwpoison_user_mappings()).
The root cause of the issue is that pte conversion to hwpoisoned entry is
now done in the first call of try_to_unmap() because PageHWPoison is
already set at this point, while it's actually expected to be done in the
second call. This behavior disturbs the error handling operation like
removing pagecache, which results in the malfunction described above.
So convert TTU_IGNORE_HWPOISON into TTU_HWPOISON and set TTU_HWPOISON only
when we really intend to convert pte to hwpoison entry. This can prevent
other callers of try_to_unmap() from accidentally converting to hwpoison
entries.
Link: https://lkml.kernel.org/r/20230221085905.1465385-1-naoya.horiguchi@linux.dev
Fixes: a42634a6c0 ("readahead: Use a folio in read_pages()")
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The TLB flushing will cost quite some CPU cycles during the folio
migration in some situations. For example, when migrate a folio of a
process with multiple active threads that run on multiple CPUs. After
batching the _unmap and _move in migrate_pages(), the TLB flushing can be
batched easily with the existing TLB flush batching mechanism. This patch
implements that.
We use the following test case to test the patch.
On a 2-socket Intel server,
- Run pmbench memory accessing benchmark
- Run `migratepages` to migrate pages of pmbench between node 0 and
node 1 back and forth.
With the patch, the TLB flushing IPI reduces 99.1% during the test and the
number of pages migrated successfully per second increases 291.7%.
Haoxin helped to test the patchset on an ARM64 server with 128 cores, 2
NUMA nodes. Test results show that the page migration performance
increases up to 78%.
NOTE: TLB flushing is batched only for normal folios, not for THP folios.
Because the overhead of TLB flushing for THP folios is much lower than
that for normal folios (about 1/512 on x86 platform).
Link: https://lkml.kernel.org/r/20230213123444.155149-9-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Tested-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
