linux-kernel - [PATCH 6/8] mm/swap: remove swap_lock to simplify si

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Date:	Mon, 27 Jan 2014 18:03:04 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	hughd@...gle.com
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Minchan Kim' <minchan@...nel.org>, shli@...nel.org,
	'Bob Liu' <bob.liu@...cle.com>, weijie.yang.kh@...il.com,
	'Heesub Shin' <heesub.shin@...sung.com>, mquzik@...hat.com,
	'Linux-MM' <linux-mm@...ck.org>,
	'linux-kernel' <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org
Subject: [PATCH 6/8] mm/swap: remove swap_lock to simplify si_swapinfo()

Consider of performance and simplicity, this patch remove swap_lock
to simplify the si_swapinfo().

Because the system info we obtain through /proc or /sys interface is
just a snapshot, we don't need a very precise freeswap and totalswap count.
Some monitor tool will get these count at per-second period, so it is good
to performance.

Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
---
 mm/swapfile.c |   15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3023172..7332c3d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2637,19 +2637,8 @@ out:
 
 void si_swapinfo(struct sysinfo *val)
 {
-	unsigned int type;
-	unsigned long nr_to_be_unused = 0;
-
-	spin_lock(&swap_lock);
-	for (type = 0; type < nr_swapfiles; type++) {
-		struct swap_info_struct *si = swap_info[type];
-
-		if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
-			nr_to_be_unused += si->inuse_pages;
-	}
-	val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
-	val->totalswap = total_swap_pages + nr_to_be_unused;
-	spin_unlock(&swap_lock);
+	val->freeswap = atomic_long_read(&nr_swap_pages);
+	val->totalswap = total_swap_pages;
 }
 
 /*
-- 
1.7.10.4


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