From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753427AbdCTItZ (ORCPT ); Mon, 20 Mar 2017 04:49:25 -0400 Received: from mga01.intel.com ([192.55.52.88]:60995 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753351AbdCTIsk (ORCPT ); Mon, 20 Mar 2017 04:48:40 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,193,1486454400"; d="scan'208";a="62567398" From: "Huang, Ying" To: Andrew Morton Cc: Andi Kleen , Dave Hansen , Shaohua Li , Rik van Riel , Huang Ying , Tim Chen , Michal Hocko , "Kirill A. Shutemov" , Vegard Nossum , Ingo Molnar , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH -v2 2/2] mm, swap: Sort swap entries before free Date: Mon, 20 Mar 2017 16:47:23 +0800 Message-Id: <20170320084732.3375-2-ying.huang@intel.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20170320084732.3375-1-ying.huang@intel.com> References: <20170320084732.3375-1-ying.huang@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Huang Ying 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. Test the patch via measuring the run time of swap_cache_free_entries() during the exit phase of the applications use much swap space. The results shows that the average run time of swap_cache_free_entries() reduced about 20% after applying the patch. Signed-off-by: Huang Ying Acked-by: Tim Chen --- mm/swapfile.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/swapfile.c b/mm/swapfile.c index 90054f3c2cdc..1628dd88da40 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -37,6 +37,7 @@ #include #include #include +#include #include #include @@ -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 +1083,7 @@ void swapcache_free_entries(swp_entry_t *entries, int n) prev = NULL; p = NULL; + 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) -- 2.11.0