linux-kernel - [PATCH 2/2] mm/swap: Remove lock_initialized flag from swap_slots

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Message-Id: <867d1fb070644e6d5f0ac7780f63e75259b82cc3.1500677066.git.tim.c.chen@linux.intel.com>
Date:   Fri, 21 Jul 2017 15:45:01 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Ying Huang <ying.huang@...el.com>,
        Wenwei Tao <wenwei.tww@...baba-inc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Hillf Danton <hillf.zj@...baba-inc.com>
Subject: [PATCH 2/2] mm/swap: Remove lock_initialized flag from swap_slots_cache

We will only reach the lock initialization code
in alloc_swap_slot_cache when the cpu's swap_slots_cache's slots
have not been allocated and swap_slots_cache has not been initialized
previously.  So the lock_initialized check is redundant and unnecessary.
Remove lock_initialized flag from swap_slots_cache to save memory.

Reported-by: Wenwei Tao <wenwei.tww@...baba-inc.com>
Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
---
 include/linux/swap_slots.h | 1 -
 mm/swap_slots.c            | 9 ++++-----
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/linux/swap_slots.h b/include/linux/swap_slots.h
index 6ef92d1..a75c30b 100644
--- a/include/linux/swap_slots.h
+++ b/include/linux/swap_slots.h
@@ -10,7 +10,6 @@
 #define THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE	(2*SWAP_SLOTS_CACHE_SIZE)
 
 struct swap_slots_cache {
-	bool		lock_initialized;
 	struct mutex	alloc_lock; /* protects slots, nr, cur */
 	swp_entry_t	*slots;
 	int		nr;
diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 4c5457c..c039e6c 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -140,11 +140,10 @@ static int alloc_swap_slot_cache(unsigned int cpu)
 	if (cache->slots || cache->slots_ret)
 		/* cache already allocated */
 		goto out;
-	if (!cache->lock_initialized) {
-		mutex_init(&cache->alloc_lock);
-		spin_lock_init(&cache->free_lock);
-		cache->lock_initialized = true;
-	}
+
+	mutex_init(&cache->alloc_lock);
+	spin_lock_init(&cache->free_lock);
+
 	cache->nr = 0;
 	cache->cur = 0;
 	cache->n_ret = 0;
-- 
2.9.4