[PATCHv5 2/3] mm: reduce atomic use on use_mm fast path
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2009-08-27 16:10:50
Also in:
kvm, linux-mm, lkml
Subsystem:
memory management, the rest · Maintainers:
Andrew Morton, Linus Torvalds
When mm switched to matches that of active mm, we don't need to increment and then drop the mm count. Making that conditional reduces contention on that cache line on SMP systems. Acked-by: Andrea Arcangeli <redacted> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- mm/mmu_context.c | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/mm/mmu_context.c b/mm/mmu_context.c
index 9989c2f..0777654 100644
--- a/mm/mmu_context.c
+++ b/mm/mmu_context.c@@ -27,13 +27,16 @@ 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); } EXPORT_SYMBOL_GPL(use_mm);
--
1.6.2.5
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