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