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Hyeonggon Yoo 63895d20d6 mm/zswap: fix inconsistency when zswap_store_page() fails 
Commit b7c0ccdfba ("mm: zswap: support large folios in zswap_store()")
skips charging any zswap entries when it failed to zswap the entire folio.

However, when some base pages are zswapped but it failed to zswap the
entire folio, the zswap operation is rolled back.  When freeing zswap
entries for those pages, zswap_entry_free() uncharges the zswap entries
that were not previously charged, causing zswap charging to become
inconsistent.

This inconsistency triggers two warnings with following steps:
  # On a machine with 64GiB of RAM and 36GiB of zswap
  $ stress-ng --bigheap 2 # wait until the OOM-killer kills stress-ng
  $ sudo reboot

  The two warnings are:
    in mm/memcontrol.c:163, function obj_cgroup_release():
      WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));

    in mm/page_counter.c:60, function page_counter_cancel():
      if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n",
	  new, nr_pages))

zswap_stored_pages also becomes inconsistent in the same way.

As suggested by Kanchana, increment zswap_stored_pages and charge zswap
entries within zswap_store_page() when it succeeds.  This way,
zswap_entry_free() will decrement the counter and uncharge the entries
when it failed to zswap the entire folio.

While this could potentially be optimized by batching objcg charging and
incrementing the counter, let's focus on fixing the bug this time and
leave the optimization for later after some evaluation.

After resolving the inconsistency, the warnings disappear.

[42.hyeyoo@gmail.com: refactor zswap_store_page()]
  Link: https://lkml.kernel.org/r/20250131082037.2426-1-42.hyeyoo@gmail.com
Link: https://lkml.kernel.org/r/20250129100844.2935-1-42.hyeyoo@gmail.com
Fixes: b7c0ccdfba ("mm: zswap: support large folios in zswap_store()")
Co-developed-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Acked-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2025-02-17 22:40:01 -08:00
arch - Explicitly clear DEBUGCTL.LBR to prevent LBRs continuing being enabled after 2025-02-16 10:41:50 -08:00
block block-6.14-20250214 2025-02-14 11:40:59 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
Documentation Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
drivers Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
fs procfs: fix a locking bug in a vmcore_add_device_dump() error path 2025-02-17 22:40:00 -08:00
include Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
init Kbuild updates for v6.14 2025-01-31 12:07:07 -08:00
io_uring io_uring-6.14-20250214 2025-02-14 11:30:53 -08:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel - Remove an unused config item GENERIC_PENDING_IRQ_CHIPFLAGS 2025-02-16 10:55:17 -08:00
lib lib/iov_iter: fix import_iovec_ubuf iovec management 2025-02-17 22:40:00 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/zswap: fix inconsistency when zswap_store_page() fails 2025-02-17 22:40:01 -08:00
net Including fixes from netfilter, wireless and bluetooth. 2025-02-13 12:17:04 -08:00
rust Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
samples Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
scripts modpost: Fix a few typos in a comment 2025-02-16 03:10:58 +09:00
security Redo of pathname patternization and fix spelling errors. 2025-02-11 10:19:36 -08:00
sound sound fixes for 6.14-rc1 2025-01-31 09:17:02 -08:00
tools - Move a warning about a lld.ld breakage into the verbose setting as said 2025-02-16 10:30:58 -08:00
usr kbuild: Drop support for include/asm-<arch> in headers_check.pl 2024-12-21 11:43:17 +09:00
virt KVM: remove kvm_arch_post_init_vm 2025-02-04 11:27:45 -05:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: use host dylib naming convention to support macOS 2025-01-10 01:01:24 +01:00
.mailmap wireless fixes for v6.14-rc3 2025-02-10 18:13:07 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Pavel to kernel.org address 2025-02-07 09:12:33 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
Makefile Linux 6.14-rc3 2025-02-16 14:02:44 -08:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.