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Andrea Arcangeli 880a99b60d mm/rmap: support move to different root anon_vma in folio_move_anon_rmap()
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>
2023-12-29 11:58:23 -08:00
arch sync mm-stable with mm-hotfixes-stable to pick up depended-upon changes 2023-12-20 14:47:18 -08:00
block fs: convert error_remove_page to error_remove_folio 2023-12-10 16:51:42 -08:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto This push fixes a regression in ahash and hides the Kconfig sub-options for the jitter RNG. 2023-11-09 17:04:58 -08:00
Documentation Docs/admin-guide/mm/damon/usage: use a list for 'state' sysfs file input commands 2023-12-20 14:48:13 -08:00
drivers list_lru: allow explicit memcg and NUMA node selection 2023-12-12 10:57:01 -08:00
fs buffer: fix more functions for block size > PAGE_SIZE 2023-12-29 11:58:23 -08:00
include gfp: gfp_types.h: fix typos & punctuation 2023-12-20 14:48:14 -08:00
init As usual, lots of singleton and doubleton patches all over the tree and 2023-11-02 20:53:31 -10:00
io_uring io_uring: use fget/fput consistently 2023-11-28 11:56:29 -07:00
ipc Many singleton patches against the MM code. The patch series which are 2023-11-02 19:38:47 -10:00
kernel sync mm-stable with mm-hotfixes-stable to pick up depended-upon changes 2023-12-20 14:47:18 -08:00
lib UBSAN: use the kernel panic message markers 2023-12-20 14:48:14 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/rmap: support move to different root anon_vma in folio_move_anon_rmap() 2023-12-29 11:58:23 -08:00
net wireless fixes: 2023-11-29 19:43:34 -08:00
rust Kbuild updates for v6.7 2023-11-04 08:07:19 -10:00
samples samples/cgroup: introduce memcg memory.events listener 2023-12-10 16:51:54 -08:00
scripts Merge branch 'master' into mm-hotfixes-stable 2023-12-06 17:03:50 -08:00
security + Features 2023-11-03 09:48:17 -10:00
sound ALSA: hda: Disable power-save on KONTRON SinglePC 2023-11-30 16:14:21 +01:00
tools selftests/damon: add a test for update_schemes_tried_regions hang bug 2023-12-20 14:48:13 -08:00
usr arch: Remove Itanium (IA-64) architecture 2023-09-11 08:13:17 +00:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: generate kernel.spec in rpmbuild/SPECS/ 2023-10-03 20:49:09 +09:00
.mailmap mailmap: add an old address for Naoya Horiguchi 2023-12-20 13:46:20 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS MAINTAINERS: drop Antti Palosaari 2023-12-06 16:12:49 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig
MAINTAINERS samples: introduce new samples subdir for cgroup 2023-12-10 16:51:54 -08:00
Makefile Linux 6.7-rc4 2023-12-03 18:52:56 +09:00
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