From e8c26ab60598558ec3a626e7925b06e7417d7710 Mon Sep 17 00:00:00 2001
From: Tim Chen <tim.c.chen@linux.intel.com>
Date: Wed, 22 Feb 2017 15:45:29 -0800
Subject: mm/swap: skip readahead for unreferenced swap slots

We can avoid needlessly allocating page for swap slots that are not used
by anyone.  No pages have to be read in for these slots.

Link: http://lkml.kernel.org/r/0784b3f20b9bd3aa5552219624cb78dc4ae710c9.1484082593.git.tim.c.chen@linux.intel.com
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Aaron Lu <aaron.lu@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net> escreveu:
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/swap_state.c | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'mm/swap_state.c')

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 3863acd6189c..3d76d80c07d6 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -323,6 +323,10 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		if (found_page)
 			break;
 
+		/* Just skip read ahead for unused swap slot */
+		if (!__swp_swapcount(entry))
+			return NULL;
+
 		/*
 		 * Get a new page to read into from swap.
 		 */
-- 
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