When mm switched to matches that of 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 cache line on SMP systems.
Acked-by: Andrea Arcangeli <[email protected]> Signed-off-by: Michael S. Tsirkin <[email protected]> --- 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 fd473b5..ded9081 100644 --- a/mm/mmu_context.c +++ b/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); } /* -- 1.6.2.5 _______________________________________________ Virtualization mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/virtualization
