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29 July 2024, 15:18:00 UTC
Revision 1b2de5d039c883c9d44ae5b2b6eca4ff9bd82dac authored by Linus Torvalds on 09 July 2018, 20:19:49 UTC, committed by Linus Torvalds on 25 August 2018, 20:15:03 UTC 
mm/cow: don't bother write protecting already write-protected pages
 
This is not normally noticeable, but repeated forks are unnecessarily
expensive because they repeatedly dirty the parent page tables during
the page table copy operation.

It's trivial to just avoid write protecting the page table entry if it
was already not writable.

This patch was inspired by

    https://bugzilla.kernel.org/show_bug.cgi?id=200447

which points to an ancient "waste time re-doing fork" issue in the
presence of lots of signals.

That bug was fixed by Eric Biederman's signal handling series
culminating in commit c3ad2c3b02e9 ("signal: Don't restart fork when
signals come in"), but the unnecessary work for repeated forks is still
work just fixing, particularly since the fix is trivial.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent e0fcfe1
History
Tip revision: 1b2de5d039c883c9d44ae5b2b6eca4ff9bd82dac authored by Linus Torvalds on 09 July 2018, 20:19:49 UTC
mm/cow: don't bother write protecting already write-protected pages
Tip revision: 1b2de5d
File Mode Size
Documentation
LICENSES
arch
block
certs
crypto
drivers
firmware
fs
include
init
ipc
kernel
lib
mm
net
samples
scripts
security
sound
tools
usr
virt
.clang-format -rw-r--r-- 12.8 KB
.cocciconfig -rw-r--r-- 59 bytes
.get_maintainer.ignore -rw-r--r-- 31 bytes
.gitattributes -rw-r--r-- 30 bytes
.gitignore -rw-r--r-- 1.5 KB
.mailmap -rw-r--r-- 9.6 KB
COPYING -rw-r--r-- 423 bytes
CREDITS -rw-r--r-- 96.4 KB
Kbuild -rw-r--r-- 2.2 KB
Kconfig -rw-r--r-- 563 bytes
MAINTAINERS -rw-r--r-- 458.4 KB
Makefile -rw-r--r-- 59.0 KB
README -rw-r--r-- 800 bytes

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