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H A D | mmap.c | diff 5f70b962ccc2f2e6259417cf3d1233dc9e16cf5e Wed May 25 02:11:19 CEST 2011 Shaohua Li <shaohua.li@intel.com> 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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