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Gabriel Krisman Bertazi 48a934fc47 Revert "mm/page_alloc.c: don't show protection in zone's ->lowmem_reserve[] for empty zone" 
commit eae116d1f0 upstream.

Commit 96a5c186ef ("mm/page_alloc.c: don't show protection in zone's
->lowmem_reserve[] for empty zone") removes the protection of lower zones
from allocations targeting memory-less high zones.  This had an unintended
impact on the pattern of reclaims because it makes the high-zone-targeted
allocation more likely to succeed in lower zones, which adds pressure to
said zones.  I.e, the following corresponding checks in
zone_watermark_ok/zone_watermark_fast are less likely to trigger:

        if (free_pages <= min + z->lowmem_reserve[highest_zoneidx])
                return false;

As a result, we are observing an increase in reclaim and kswapd scans, due
to the increased pressure.  This was initially observed as increased
latency in filesystem operations when benchmarking with fio on a machine
with some memory-less zones, but it has since been associated with
increased contention in locks related to memory reclaim.  By reverting
this patch, the original performance was recovered on that machine.

The original commit was introduced as a clarification of the
/proc/zoneinfo output, so it doesn't seem there are usecases depending on
it, making the revert a simple solution.

For reference, I collected vmstat with and without this patch on a freshly
booted system running intensive randread io from an nvme for 5 minutes.  I
got:

rpm-6.12.0-slfo.1.2 ->  pgscan_kswapd 5629543865
Patched             ->  pgscan_kswapd 33580844

33M scans is similar to what we had in kernels predating this patch.
These numbers is fairly representative of the workload on this machine, as
measured in several runs.  So we are talking about a 2-order of magnitude
increase.

Link: https://lkml.kernel.org/r/20250226032258.234099-1-krisman@suse.de
Fixes: 96a5c186ef ("mm/page_alloc.c: don't show protection in zone's ->lowmem_reserve[] for empty zone")
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-03-13 13:01:54 +01:00
arch LoongArch: KVM: Fix GPA size issue about VM 2025-03-13 13:01:50 +01:00
block block: Remove zone write plugs when handling native zone append writes 2025-03-07 18:25:40 +01:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: api - Fix boot-up self-test race 2025-02-08 09:57:28 +01:00
Documentation Documentation: rust: discuss #[expect(...)] in the guidelines 2025-03-13 13:01:42 +01:00
drivers drm/radeon: Fix rs400_gpu_init for ATI mobility radeon Xpress 200M 2025-03-13 13:01:53 +01:00
fs btrfs: fix a leaked chunk map issue in read_one_chunk() 2025-03-13 13:01:52 +01:00
include rcuref: Plug slowpath race in rcuref_put() 2025-03-07 18:25:43 +01:00
init Compiler Attributes: disable __counted_by for clang < 19.1.3 2024-12-05 14:02:45 +01:00
io_uring io_uring/net: save msg_control for compat 2025-03-07 18:25:35 +01:00
ipc ipc: fix memleak if msg_init_ns failed in create_ipc_ns 2024-12-05 14:03:02 +01:00
kernel tracing: tprobe-events: Reject invalid tracepoint name 2025-03-13 13:01:49 +01:00
lib rcuref: Plug slowpath race in rcuref_put() 2025-03-07 18:25:43 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm
net mptcp: reset when MPTCP opts are dropped after join 2025-03-07 18:25:42 +01:00
rust rust: alloc: Fix ArrayLayout allocations 2025-03-13 13:01:49 +01:00
samples rust: treewide: switch to the kernel Vec type 2025-03-13 13:01:46 +01:00
scripts kbuild: rust: remove the alloc crate and GlobalAlloc 2025-03-13 13:01:47 +01:00
security ima: Reset IMA_NONACTION_RULE_FLAGS after post_setattr 2025-03-07 18:25:44 +01:00
sound ALSA: hda/realtek: update ALC222 depop optimize 2025-03-13 13:01:52 +01:00
tools rseq/selftests: Fix riscv rseq_offset_deref_addv inline asm 2025-03-07 18:25:44 +01:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt KVM: x86: switch hugepage recovery thread to vhost_task 2024-12-05 14:02:43 +01:00
.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: enable Clippy's check-private-items 2025-03-13 13:01:42 +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 Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -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: Remove self from DSA entry 2024-11-03 12:52:38 -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 MAINTAINERS: add entry for the Rust alloc module 2025-03-13 13:01:47 +01:00
Makefile rust: replace clippy::dbg_macro with disallowed_macros 2025-03-13 13:01:42 +01:00
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.