df3e764d8e
Loading modules with finit_module() can end up using vmalloc(), vmap()
and vmalloc() again, for a total of up to 3 separate allocations in the
worst case for a single module. We always kernel_read*() the module,
that's a vmalloc(). Then vmap() is used for the module decompression,
and if so the last read buffer is freed as we use the now decompressed
module buffer to stuff data into our copy module. The last allocation is
specific to each architectures but pretty much that's generally a series
of vmalloc() calls or a variation of vmalloc to handle ELF sections with
special permissions.
Evaluation with new stress-ng module support [1] with just 100 ops
is proving that you can end up using GiBs of data easily even with all
care we have in the kernel and userspace today in trying to not load modules
which are already loaded. 100 ops seems to resemble the sort of pressure a
system with about 400 CPUs can create on module loading. Although issues
relating to duplicate module requests due to each CPU inucurring a new
module reuest is silly and some of these are being fixed, we currently lack
proper tooling to help diagnose easily what happened, when it happened
and who likely is to blame -- userspace or kernel module autoloading.
Provide an initial set of stats which use debugfs to let us easily scrape
post-boot information about failed loads. This sort of information can
be used on production worklaods to try to optimize *avoiding* redundant
memory pressure using finit_module().
There's a few examples that can be provided:
A 255 vCPU system without the next patch in this series applied:
Startup finished in 19.143s (kernel) + 7.078s (userspace) = 26.221s
graphical.target reached after 6.988s in userspace
And 13.58 GiB of virtual memory space lost due to failed module loading:
root@big ~ # cat /sys/kernel/debug/modules/stats
Mods ever loaded 67
Mods failed on kread 0
Mods failed on decompress 0
Mods failed on becoming 0
Mods failed on load 1411
Total module size 11464704
Total mod text size 4194304
Failed kread bytes 0
Failed decompress bytes 0
Failed becoming bytes 0
Failed kmod bytes 14588526272
Virtual mem wasted bytes 14588526272
Average mod size 171115
Average mod text size 62602
Average fail load bytes 10339140
Duplicate failed modules:
module-name How-many-times Reason
kvm_intel 249 Load
kvm 249 Load
irqbypass 8 Load
crct10dif_pclmul 128 Load
ghash_clmulni_intel 27 Load
sha512_ssse3 50 Load
sha512_generic 200 Load
aesni_intel 249 Load
crypto_simd 41 Load
cryptd 131 Load
evdev 2 Load
serio_raw 1 Load
virtio_pci 3 Load
nvme 3 Load
nvme_core 3 Load
virtio_pci_legacy_dev 3 Load
virtio_pci_modern_dev 3 Load
t10_pi 3 Load
virtio 3 Load
crc32_pclmul 6 Load
crc64_rocksoft 3 Load
crc32c_intel 40 Load
virtio_ring 3 Load
crc64 3 Load
The following screen shot, of a simple 8vcpu 8 GiB KVM guest with the
next patch in this series applied, shows 226.53 MiB are wasted in virtual
memory allocations which due to duplicate module requests during boot.
It also shows an average module memory size of 167.10 KiB and an an
average module .text + .init.text size of 61.13 KiB. The end shows all
modules which were detected as duplicate requests and whether or not
they failed early after just the first kernel_read*() call or late after
we've already allocated the private space for the module in
layout_and_allocate(). A system with module decompression would reveal
more wasted virtual memory space.
We should put effort now into identifying the source of these duplicate
module requests and trimming these down as much possible. Larger systems
will obviously show much more wasted virtual memory allocations.
root@kmod ~ # cat /sys/kernel/debug/modules/stats
Mods ever loaded 67
Mods failed on kread 0
Mods failed on decompress 0
Mods failed on becoming 83
Mods failed on load 16
Total module size 11464704
Total mod text size 4194304
Failed kread bytes 0
Failed decompress bytes 0
Failed becoming bytes 228959096
Failed kmod bytes 8578080
Virtual mem wasted bytes 237537176
Average mod size 171115
Average mod text size 62602
Avg fail becoming bytes 2758544
Average fail load bytes 536130
Duplicate failed modules:
module-name How-many-times Reason
kvm_intel 7 Becoming
kvm 7 Becoming
irqbypass 6 Becoming & Load
crct10dif_pclmul 7 Becoming & Load
ghash_clmulni_intel 7 Becoming & Load
sha512_ssse3 6 Becoming & Load
sha512_generic 7 Becoming & Load
aesni_intel 7 Becoming
crypto_simd 7 Becoming & Load
cryptd 3 Becoming & Load
evdev 1 Becoming
serio_raw 1 Becoming
nvme 3 Becoming
nvme_core 3 Becoming
t10_pi 3 Becoming
virtio_pci 3 Becoming
crc32_pclmul 6 Becoming & Load
crc64_rocksoft 3 Becoming
crc32c_intel 3 Becoming
virtio_pci_modern_dev 2 Becoming
virtio_pci_legacy_dev 1 Becoming
crc64 2 Becoming
virtio 2 Becoming
virtio_ring 2 Becoming
[0] https://github.com/ColinIanKing/stress-ng.git
[1] echo 0 > /proc/sys/vm/oom_dump_tasks
./stress-ng --module 100 --module-name xfs
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
415 lines
8.6 KiB
ReStructuredText
415 lines
8.6 KiB
ReStructuredText
====================
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The Linux Kernel API
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====================
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List Management Functions
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=========================
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.. kernel-doc:: include/linux/list.h
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:internal:
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Basic C Library Functions
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=========================
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When writing drivers, you cannot in general use routines which are from
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the C Library. Some of the functions have been found generally useful
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and they are listed below. The behaviour of these functions may vary
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slightly from those defined by ANSI, and these deviations are noted in
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the text.
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String Conversions
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------------------
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.. kernel-doc:: lib/vsprintf.c
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:export:
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.. kernel-doc:: include/linux/kstrtox.h
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:functions: kstrtol kstrtoul
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.. kernel-doc:: lib/kstrtox.c
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:export:
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.. kernel-doc:: lib/string_helpers.c
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:export:
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String Manipulation
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-------------------
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.. kernel-doc:: include/linux/fortify-string.h
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:internal:
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.. kernel-doc:: lib/string.c
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:export:
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.. kernel-doc:: include/linux/string.h
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:internal:
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.. kernel-doc:: mm/util.c
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:functions: kstrdup kstrdup_const kstrndup kmemdup kmemdup_nul memdup_user
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vmemdup_user strndup_user memdup_user_nul
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Basic Kernel Library Functions
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==============================
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The Linux kernel provides more basic utility functions.
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Bit Operations
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--------------
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.. kernel-doc:: include/asm-generic/bitops/instrumented-atomic.h
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:internal:
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.. kernel-doc:: include/asm-generic/bitops/instrumented-non-atomic.h
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:internal:
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.. kernel-doc:: include/asm-generic/bitops/instrumented-lock.h
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:internal:
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Bitmap Operations
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-----------------
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.. kernel-doc:: lib/bitmap.c
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:doc: bitmap introduction
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.. kernel-doc:: include/linux/bitmap.h
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:doc: declare bitmap
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.. kernel-doc:: include/linux/bitmap.h
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:doc: bitmap overview
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.. kernel-doc:: include/linux/bitmap.h
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:doc: bitmap bitops
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.. kernel-doc:: lib/bitmap.c
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:export:
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.. kernel-doc:: lib/bitmap.c
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:internal:
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.. kernel-doc:: include/linux/bitmap.h
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:internal:
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Command-line Parsing
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--------------------
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.. kernel-doc:: lib/cmdline.c
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:export:
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Sorting
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-------
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.. kernel-doc:: lib/sort.c
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:export:
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.. kernel-doc:: lib/list_sort.c
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:export:
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Text Searching
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--------------
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.. kernel-doc:: lib/textsearch.c
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:doc: ts_intro
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.. kernel-doc:: lib/textsearch.c
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:export:
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.. kernel-doc:: include/linux/textsearch.h
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:functions: textsearch_find textsearch_next \
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textsearch_get_pattern textsearch_get_pattern_len
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CRC and Math Functions in Linux
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===============================
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Arithmetic Overflow Checking
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----------------------------
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.. kernel-doc:: include/linux/overflow.h
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:internal:
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CRC Functions
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-------------
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.. kernel-doc:: lib/crc4.c
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:export:
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.. kernel-doc:: lib/crc7.c
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:export:
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.. kernel-doc:: lib/crc8.c
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:export:
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.. kernel-doc:: lib/crc16.c
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:export:
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.. kernel-doc:: lib/crc32.c
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.. kernel-doc:: lib/crc-ccitt.c
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:export:
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.. kernel-doc:: lib/crc-itu-t.c
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:export:
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Base 2 log and power Functions
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------------------------------
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.. kernel-doc:: include/linux/log2.h
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:internal:
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Integer power Functions
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-----------------------
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.. kernel-doc:: lib/math/int_pow.c
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:export:
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.. kernel-doc:: lib/math/int_sqrt.c
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:export:
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Division Functions
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------------------
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.. kernel-doc:: include/asm-generic/div64.h
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:functions: do_div
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.. kernel-doc:: include/linux/math64.h
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:internal:
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.. kernel-doc:: lib/math/gcd.c
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:export:
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UUID/GUID
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---------
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.. kernel-doc:: lib/uuid.c
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:export:
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Kernel IPC facilities
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=====================
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IPC utilities
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-------------
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.. kernel-doc:: ipc/util.c
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:internal:
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FIFO Buffer
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===========
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kfifo interface
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---------------
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.. kernel-doc:: include/linux/kfifo.h
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:internal:
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relay interface support
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=======================
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Relay interface support is designed to provide an efficient mechanism
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for tools and facilities to relay large amounts of data from kernel
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space to user space.
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relay interface
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---------------
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.. kernel-doc:: kernel/relay.c
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:export:
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.. kernel-doc:: kernel/relay.c
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:internal:
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Module Support
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==============
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Kernel module auto-loading
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--------------------------
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.. kernel-doc:: kernel/module/kmod.c
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:export:
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Module debugging
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----------------
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.. kernel-doc:: kernel/module/stats.c
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:doc: module debugging statistics overview
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dup_failed_modules - tracks duplicate failed modules
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****************************************************
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.. kernel-doc:: kernel/module/stats.c
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:doc: dup_failed_modules - tracks duplicate failed modules
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module statistics debugfs counters
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**********************************
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.. kernel-doc:: kernel/module/stats.c
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:doc: module statistics debugfs counters
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Inter Module support
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--------------------
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Refer to the files in kernel/module/ for more information.
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Hardware Interfaces
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===================
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DMA Channels
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------------
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.. kernel-doc:: kernel/dma.c
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:export:
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Resources Management
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--------------------
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.. kernel-doc:: kernel/resource.c
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:internal:
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.. kernel-doc:: kernel/resource.c
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:export:
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MTRR Handling
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-------------
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.. kernel-doc:: arch/x86/kernel/cpu/mtrr/mtrr.c
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:export:
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Security Framework
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==================
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.. kernel-doc:: security/security.c
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:internal:
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.. kernel-doc:: security/inode.c
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:export:
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Audit Interfaces
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================
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.. kernel-doc:: kernel/audit.c
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:export:
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.. kernel-doc:: kernel/auditsc.c
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:internal:
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.. kernel-doc:: kernel/auditfilter.c
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:internal:
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Accounting Framework
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====================
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.. kernel-doc:: kernel/acct.c
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:internal:
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Block Devices
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=============
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.. kernel-doc:: include/linux/bio.h
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.. kernel-doc:: block/blk-core.c
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:export:
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.. kernel-doc:: block/blk-core.c
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:internal:
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.. kernel-doc:: block/blk-map.c
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:export:
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.. kernel-doc:: block/blk-sysfs.c
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:internal:
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.. kernel-doc:: block/blk-settings.c
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:export:
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.. kernel-doc:: block/blk-flush.c
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:export:
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.. kernel-doc:: block/blk-lib.c
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:export:
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.. kernel-doc:: block/blk-integrity.c
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:export:
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.. kernel-doc:: kernel/trace/blktrace.c
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:internal:
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.. kernel-doc:: block/genhd.c
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:internal:
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.. kernel-doc:: block/genhd.c
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:export:
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.. kernel-doc:: block/bdev.c
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:export:
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Char devices
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============
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.. kernel-doc:: fs/char_dev.c
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:export:
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Clock Framework
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===============
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The clock framework defines programming interfaces to support software
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management of the system clock tree. This framework is widely used with
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System-On-Chip (SOC) platforms to support power management and various
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devices which may need custom clock rates. Note that these "clocks"
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don't relate to timekeeping or real time clocks (RTCs), each of which
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have separate frameworks. These :c:type:`struct clk <clk>`
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instances may be used to manage for example a 96 MHz signal that is used
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to shift bits into and out of peripherals or busses, or otherwise
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trigger synchronous state machine transitions in system hardware.
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Power management is supported by explicit software clock gating: unused
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clocks are disabled, so the system doesn't waste power changing the
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state of transistors that aren't in active use. On some systems this may
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be backed by hardware clock gating, where clocks are gated without being
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disabled in software. Sections of chips that are powered but not clocked
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may be able to retain their last state. This low power state is often
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called a *retention mode*. This mode still incurs leakage currents,
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especially with finer circuit geometries, but for CMOS circuits power is
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mostly used by clocked state changes.
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Power-aware drivers only enable their clocks when the device they manage
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is in active use. Also, system sleep states often differ according to
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which clock domains are active: while a "standby" state may allow wakeup
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from several active domains, a "mem" (suspend-to-RAM) state may require
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a more wholesale shutdown of clocks derived from higher speed PLLs and
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oscillators, limiting the number of possible wakeup event sources. A
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driver's suspend method may need to be aware of system-specific clock
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constraints on the target sleep state.
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Some platforms support programmable clock generators. These can be used
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by external chips of various kinds, such as other CPUs, multimedia
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codecs, and devices with strict requirements for interface clocking.
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.. kernel-doc:: include/linux/clk.h
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:internal:
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Synchronization Primitives
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==========================
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Read-Copy Update (RCU)
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----------------------
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.. kernel-doc:: include/linux/rcupdate.h
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.. kernel-doc:: kernel/rcu/tree.c
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.. kernel-doc:: kernel/rcu/tree_exp.h
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.. kernel-doc:: kernel/rcu/update.c
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.. kernel-doc:: include/linux/srcu.h
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.. kernel-doc:: kernel/rcu/srcutree.c
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.. kernel-doc:: include/linux/rculist_bl.h
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.. kernel-doc:: include/linux/rculist.h
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.. kernel-doc:: include/linux/rculist_nulls.h
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.. kernel-doc:: include/linux/rcu_sync.h
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.. kernel-doc:: kernel/rcu/sync.c
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