[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>
diff --git a/mm/memory.c b/mm/memory.c
index 9abc600..85e80a5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -623,11 +623,12 @@
(*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) {
/*
