The patch titled
mm: reduce atomic use on use_mm fast path
has been added to the -mm tree. Its filename is
mm-reduce-atomic-use-on-use_mm-fast-path.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: mm: reduce atomic use on use_mm fast path
From: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
When the mm being switched to matches the active mm, we don't need to
increment and then drop the mm count. In a simple benchmark this happens
in about 50% of time. Making that conditional reduces contention on that
cacheline on SMP systems.
Acked-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmu_context.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff -puN mm/mmu_context.c~mm-reduce-atomic-use-on-use_mm-fast-path mm/mmu_context.c
--- a/mm/mmu_context.c~mm-reduce-atomic-use-on-use_mm-fast-path
+++ a/mm/mmu_context.c
@@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm)
task_lock(tsk);
active_mm = tsk->active_mm;
- atomic_inc(&mm->mm_count);
+ if (active_mm != mm) {
+ atomic_inc(&mm->mm_count);
+ tsk->active_mm = mm;
+ }
tsk->mm = mm;
- tsk->active_mm = mm;
switch_mm(active_mm, mm, tsk);
task_unlock(tsk);
- mmdrop(active_mm);
+ if (active_mm != mm)
+ mmdrop(active_mm);
}
/*
_
Patches currently in -mm which might be from mst@xxxxxxxxxx are
origin.patch
linux-next.patch
mm-move-use_mm-unuse_mm-from-aioc-to-mm.patch
mm-reduce-atomic-use-on-use_mm-fast-path.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
