kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-10-26 19:14:18 +00:00
Code Issues Releases Packages Activity
No description
1,397,934 commits 117 branches 5,805 tags 5.9 GiB
  • C 96.8%
  • Assembly 0.9%
  • Rust 0.7%
  • Shell 0.6%
  • Python 0.5%
  • Other 0.3%
Find a file
Roman Gushchin 9f1edf1aed mm: readahead: make thp readahead conditional to mmap_miss logic 
Commit 4687fdbb80 ("mm/filemap: Support VM_HUGEPAGE for file mappings")
introduced a special handling for VM_HUGEPAGE mappings: even if the
readahead is disabled, 1 or 2 HPAGE_PMD_ORDER pages are allocated.

This change causes a significant regression for containers with a tight
memory.max limit, if VM_HUGEPAGE is widely used.  Prior to this commit,
mmap_miss logic would eventually lead to the readahead disablement,
effectively reducing the memory pressure in the cgroup.  With this change
the kernel is trying to allocate 1-2 huge pages for each fault, no matter
if these pages are used or not before being evicted, increasing the memory
pressure multi-fold.

To fix the regression, let's make the new VM_HUGEPAGE conditional to the
mmap_miss check, but keep independent from the ra->ra_pages.  This way the
main intention of commit 4687fdbb80 ("mm/filemap: Support VM_HUGEPAGE
for file mappings") stays intact, but the regression is resolved.

The logic behind this changes is simple: even if a user explicitly
requests using huge pages to back the file mapping (using VM_HUGEPAGE
flag), under a very strong memory pressure it's better to fall back to
ordinary pages.

Link: https://lkml.kernel.org/r/20251006175106.377411-1-roman.gushchin@linux.dev
Fixes: 4687fdbb80 ("mm/filemap: Support VM_HUGEPAGE for file mappings")
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
History 2025-11-16 17:27:56 -08:00
arch
block
certs
crypto
Documentation
drivers
fs
include
init
io_uring
ipc
kernel
lib
LICENSES
mm
net
rust
samples
scripts
security
sound
tools
usr
virt
.clang-format
.clippy.toml
.cocciconfig
.editorconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
.pylintrc
.rustfmt.toml
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile
README

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.