diff options
authorHugh Dickins <>2006-03-16 23:04:09 -0800
committerLinus Torvalds <>2006-03-17 07:51:26 -0800
commit6f5e6b9e69bf043074a0edabe3d271899c34eb79 (patch)
parent7670f023aabd976c25862e4c6fb9f6d9d2758153 (diff)
[PATCH] fix free swap cache latency
Lee Revell reported 28ms latency when process with lots of swapped memory exits. 2.6.15 introduced a latency regression when unmapping: in accounting the zap_work latency breaker, pte_none counted 1, pte_present PAGE_SIZE, but a swap entry counted nothing at all. We think of pages present as the slow case, but Lee's trace shows that free_swap_and_cache's radix tree lookup can make a lot of work - and we could have been doing it many thousands of times without a latency break. Move the zap_work update up to account swap entries like pages present. This does account non-linear pte_file entries, and unmap_mapping_range skipping over swap entries, by the same amount even though they're quick: but neither of those cases deserves complicating the code (and they're treated no worse than they were in 2.6.14). Signed-off-by: Hugh Dickins <> Acked-by: Nick Piggin <> Acked-by: Ingo Molnar <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
1 files changed, 3 insertions, 2 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 9abc6008544..85e80a57db2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -623,11 +623,12 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
+ (*zap_work) -= PAGE_SIZE;
if (pte_present(ptent)) {
struct page *page;
- (*zap_work) -= PAGE_SIZE;
page = vm_normal_page(vma, addr, ptent);
if (unlikely(details) && page) {