diff options
author | Huang Ying <ying.huang@intel.com> | 2017-05-31 09:17:22 +1000 |
---|---|---|
committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2017-06-01 08:39:42 +1000 |
commit | 7b1e14fa1b0d3cb5e0793ba0f3712f3d8235ac8a (patch) | |
tree | c877ce01cecb3e7e000e83f8bf953db3ecaa401e /mm | |
parent | 573b9107bf7b7b4d10180191f9ef50dbfce639c7 (diff) |
mm/swapfile.c: 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.
With the patch, the memory (some swapped out) free time reduced 11.6%
(from 2.65s to 2.35s) in the vm-scalability swap-w-rand test case with 16
processes. The test is done on a Xeon E5 v3 system. The swap device used
is a RAM simulated PMEM (persistent memory) device. To test swapping, the
test case creates 16 processes, which allocate and write to the anonymous
pages until the RAM and part of the swap device is used up, finally the
memory (some swapped out) is freed before exit.
Link: http://lkml.kernel.org/r/20170525005916.25249-1-ying.huang@intel.com
Signed-off-by: Huang Ying <ying.huang@intel.com>
Acked-by: Tim Chen <tim.c.chen@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/swapfile.c | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c index 9d7e9ad2447e..5242d25bf4a5 100644 --- a/mm/swapfile.c +++ b/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> @@ -1198,6 +1199,13 @@ void put_swap_page(struct page *page, swp_entry_t entry) swapcache_free_cluster(entry); } +static int swp_entry_cmp(const void *ent1, const void *ent2) +{ + const swp_entry_t *e1 = ent1, *e2 = ent2; + + return (int)swp_type(*e1) - (int)swp_type(*e2); +} + void swapcache_free_entries(swp_entry_t *entries, int n) { struct swap_info_struct *p, *prev; @@ -1208,6 +1216,15 @@ void swapcache_free_entries(swp_entry_t *entries, int n) prev = NULL; p = NULL; + + /* + * Sort swap entries by swap device, so each lock is only + * taken once. Although nr_swapfiles isn't absolute correct, + * but the overhead of sort() is so low that it isn't + * necessary to optimize further. + */ + 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) |