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Wei Yang 4e4a9eb921 mm/rmap.c: reuse mergeable anon_vma as parent when fork 
In __anon_vma_prepare(), we will try to find anon_vma if it is possible to
reuse it.  While on fork, the logic is different.

Since commit 5beb493052 ("mm: change anon_vma linking to fix
multi-process server scalability issue"), function anon_vma_clone() tries
to allocate new anon_vma for child process.  But the logic here will
allocate a new anon_vma for each vma, even in parent this vma is mergeable
and share the same anon_vma with its sibling.  This may do better for
scalability issue, while it is not necessary to do so especially after
interval tree is used.

Commit 7a3ef208e6 ("mm: prevent endless growth of anon_vma hierarchy")
tries to reuse some anon_vma by counting child anon_vma and attached vmas.
While for those mergeable anon_vmas, we can just reuse it and not
necessary to go through the logic.

After this change, kernel build test reduces 20% anon_vma allocation.

Do the same kernel build test, it shows run time in sys reduced 11.6%.

Origin:

real    2m50.467s
user    17m52.002s
sys     1m51.953s

real    2m48.662s
user    17m55.464s
sys     1m50.553s

real    2m51.143s
user    17m59.687s
sys     1m53.600s

Patched:

real	2m39.933s
user	17m1.835s
sys	1m38.802s

real	2m39.321s
user	17m1.634s
sys	1m39.206s

real	2m39.575s
user	17m1.420s
sys	1m38.845s

Link: http://lkml.kernel.org/r/20191011072256.16275-2-richardw.yang@linux.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-01 06:29:19 -08:00
arch dma-mapping updates for 5.5-rc1 2019-11-28 11:16:43 -08:00
block for-5.5/disk-revalidate-20191122 2019-11-25 11:37:01 -08:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2019-11-25 19:49:58 -08:00
Documentation Documentation/admin-guide/cgroup-v2.rst: document why inactive_X + active_X may not equal X 2019-12-01 06:29:18 -08:00
drivers hmm related patches for 5.5 2019-11-30 10:33:14 -08:00
fs fs/direct-io.c: keep dio_warn_stale_pagecache() when CONFIG_BLOCK=n 2019-12-01 06:29:18 -08:00
include rss_stat: add support to detect RSS updates of external mm 2019-12-01 06:29:18 -08:00
init Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2019-11-25 20:02:57 -08:00
ipc ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
kernel hmm related patches for 5.5 2019-11-30 10:33:14 -08:00
lib rss_stat: add support to detect RSS updates of external mm 2019-12-01 06:29:18 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/rmap.c: reuse mergeable anon_vma as parent when fork 2019-12-01 06:29:19 -08:00
net for-5.5/io_uring-post-20191128 2019-11-28 10:43:39 -08:00
samples New tracing features: 2019-11-27 11:42:01 -08:00
scripts scripts/spelling.txt: add more spellings to spelling.txt 2019-12-01 06:29:17 -08:00
security drm main pull for 5.5-rc1 2019-11-27 17:45:48 -08:00
sound sound updates for 5.5-rc1 2019-11-26 20:04:35 -08:00
tools New tracing features: 2019-11-27 11:42:01 -08:00
usr kbuild: update compile-test header list for v5.4-rc2 2019-10-05 15:29:49 +09:00
virt KVM: Fix jump label out_free_* in kvm_init() 2019-11-23 11:29:17 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap Merge branch 'efi-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-11-26 14:52:11 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS \n 2019-11-30 11:34:33 -08:00
Makefile Linux 5.4 2019-11-24 16:32:01 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.