From 6f5e6b9e69bf043074a0edabe3d271899c34eb79 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hugh@veritas.com>
Date: Thu, 16 Mar 2006 23:04:09 -0800
Subject: [PATCH] [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 <hugh@veritas.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
mm/memory.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 9abc6008544baa..85e80a57db29e2 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)--;
continue;
}
+
+ (*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) {
/*
--
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