The patch titled
Subject: mm, swap: sort swap entries before free
has been added to the -mm tree. Its filename is
mm-swap-sort-swap-entries-before-free.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-sort-swap-entries-before-free.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-swap-sort-swap-entries-before-free.patch
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------------------------------------------------------
From: Huang Ying <ying.huang@xxxxxxxxx>
Subject: mm, swap: sort swap entries before free
To reduce the lock contention of swap_info_struct->lock when freeing swap
entry. The freed swap entries will be collected in a per-CPU buffer
firstly, and be really freed later in batch. During the batch freeing, if
the consecutive swap entries in the per-CPU buffer belongs to same swap
device, the swap_info_struct->lock needs to be acquired/released only
once, so that the lock contention could be reduced greatly. But if there
are multiple swap devices, it is possible that the lock may be
unnecessarily released/acquired because the swap entries belong to the
same swap device are non-consecutive in the per-CPU buffer.
To solve the issue, the per-CPU buffer is sorted according to the swap
device before freeing the swap entries. Test shows that the time spent by
swapcache_free_entries() could be reduced after the patch.
The patch was tested by measuring the run time of
swap_cache_free_entries() during the exit phase of an application which
uses much swap space. The results show that the average run time of
swap_cache_free_entries() was reduced about 20% after applying the patch.
Link: http://lkml.kernel.org/r/20170407064901.25398-1-ying.huang@xxxxxxxxx
Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>
Acked-by: Tim Chen <tim.c.chen@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swapfile.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff -puN mm/swapfile.c~mm-swap-sort-swap-entries-before-free mm/swapfile.c
--- a/mm/swapfile.c~mm-swap-sort-swap-entries-before-free
+++ a/mm/swapfile.c
@@ -37,6 +37,7 @@
#include <linux/swapfile.h>
#include <linux/export.h>
#include <linux/swap_slots.h>
+#include <linux/sort.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
@@ -1065,6 +1066,13 @@ void swapcache_free(swp_entry_t entry)
}
}
+static int swp_entry_cmp(const void *ent1, const void *ent2)
+{
+ const swp_entry_t *e1 = ent1, *e2 = ent2;
+
+ return (long)(swp_type(*e1) - swp_type(*e2));
+}
+
void swapcache_free_entries(swp_entry_t *entries, int n)
{
struct swap_info_struct *p, *prev;
@@ -1075,6 +1083,10 @@ void swapcache_free_entries(swp_entry_t
prev = NULL;
p = NULL;
+
+ /* Sort swap entries by swap device, so each lock is only taken once. */
+ if (nr_swapfiles > 1)
+ sort(entries, n, sizeof(entries[0]), swp_entry_cmp, NULL);
for (i = 0; i < n; ++i) {
p = swap_info_get_cont(entries[i], prev);
if (p)
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
mm-swap-fix-a-race-in-free_swap_and_cache.patch
mm-swap-fix-comment-in-__read_swap_cache_async.patch
mm-swap-improve-readability-via-make-spin_lock-unlock-balanced.patch
mm-swap-avoid-lock-swap_avail_lock-when-held-cluster-lock.patch
mm-swap-remove-unused-function-prototype.patch
mm-swap-use-kvzalloc-to-allocate-some-swap-data-structure.patch
mm-swap-sort-swap-entries-before-free.patch
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