mmu_gather: fix over-eager tlb_flush_mmu_free() calling

Dave Hansen reports that commit fb7332a ("mmu_gather: move minimal range calculations into generic code") caused a performance problem: "tlb_finish_mmu() goes up about 9x in the profiles (~0.4%->3.6%) and tlb_flush_mmu_free() takes about 3.1% of CPU time with the patch applied, but does not show up at all on the commit before" and the reason is that Will moved the test for whether we need to flush from tlb_flush_mmu() into tlb_flush_mmu_tlbonly(). But that meant that tlb_flush_mmu_free() basically lost that check. Move it back into tlb_flush_mmu() where it belongs, so that it covers both tlb_flush_mmu_tlbonly() _and_ tlb_flush_mmu_free(). Reported-and-tested-by: Dave Hansen <[email protected]> Acked-by: Will Deacon <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
kyagi · Dec 17, 2014 · f045bbb · f045bbb
1 parent cf3c0a1
commit f045bbb
Showing 1 changed file with 3 additions and 3 deletions.
diff --git a/mm/memory.c b/mm/memory.c
@@ -235,9 +235,6 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned long
 
 static void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 {
-	if (!tlb->end)
-		return;
-
 	tlb_flush(tlb);
 	mmu_notifier_invalidate_range(tlb->mm, tlb->start, tlb->end);
 #ifdef CONFIG_HAVE_RCU_TABLE_FREE
@@ -259,6 +256,9 @@ static void tlb_flush_mmu_free(struct mmu_gather *tlb)
 
 void tlb_flush_mmu(struct mmu_gather *tlb)
 {
+	if (!tlb->end)
+		return;
+
 	tlb_flush_mmu_tlbonly(tlb);
 	tlb_flush_mmu_free(tlb);
 }