From: Shaohua Li <shaohua.li@intel.com>
Date: Wed, 25 May 2011 00:11:19 +0000 (-0700)
Subject: mmap: avoid unnecessary anon_vma lock
X-Git-Tag: v3.0-rc1~296
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5f70b962ccc2f2e6259417cf3d1233dc9e16cf5e;p=pandora-kernel.git

mmap: avoid unnecessary anon_vma lock

If we only change vma->vm_end, we can avoid taking anon_vma lock even if
'insert' isn't NULL, which is the case of split_vma.

As I understand it, we need the lock before because rmap must get the
'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked
to anon_vma list in __insert_vm_struct before).

But now this isn't true any more.  The 'insert' VMA is already linked to
anon_vma list in __split_vma(with anon_vma_clone()) instead of
__insert_vm_struct.  There is no race rmap can't get required VMAs.  So
the anon_vma lock is unnecessary, and this can reduce one locking in brk
case and improve scalability.

Signed-off-by: Shaohua Li<shaohua.li@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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