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[109.152.100.189]) by smtp.gmail.com with ESMTPSA id q19sm3693742ejz.90.2020.11.22.07.39.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Nov 2020 07:39:07 -0800 (PST) From: Pavel Begunkov To: Jens Axboe , linux-block@vger.kernel.org, Omar Sandoval Cc: linux-kernel@vger.kernel.org Subject: [PATCH v2 2/4] sbitmap: remove swap_lock Date: Sun, 22 Nov 2020 15:35:46 +0000 Message-Id: <488177c02dccda60c5e8af2e53156c42b7f1acc0.1606058975.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.24.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org map->swap_lock protects map->cleared from concurrent modification, however sbitmap_deferred_clear() is already atomically drains it, so it's guaranteed to not loose bits on concurrent sbitmap_deferred_clear(). A one threaded tag heavy test on top of nullbk showed ~1.5% t-put increase, and 3% -> 1% cycle reduction of sbitmap_get() according to perf. Signed-off-by: Pavel Begunkov --- include/linux/sbitmap.h | 5 ----- lib/sbitmap.c | 14 +++----------- 2 files changed, 3 insertions(+), 16 deletions(-) diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h index e40d019c3d9d..74cc6384715e 100644 --- a/include/linux/sbitmap.h +++ b/include/linux/sbitmap.h @@ -32,11 +32,6 @@ struct sbitmap_word { * @cleared: word holding cleared bits */ unsigned long cleared ____cacheline_aligned_in_smp; - - /** - * @swap_lock: Held while swapping word <-> cleared - */ - spinlock_t swap_lock; } ____cacheline_aligned_in_smp; /** diff --git a/lib/sbitmap.c b/lib/sbitmap.c index c1c8a4e69325..4fd877048ba8 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -15,13 +15,9 @@ static inline bool sbitmap_deferred_clear(struct sbitmap_word *map) { unsigned long mask, val; - bool ret = false; - unsigned long flags; - spin_lock_irqsave(&map->swap_lock, flags); - - if (!map->cleared) - goto out_unlock; + if (!READ_ONCE(map->cleared)) + return false; /* * First get a stable cleared mask, setting the old mask to 0. @@ -35,10 +31,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap_word *map) val = map->word; } while (cmpxchg(&map->word, val, val & ~mask) != val); - ret = true; -out_unlock: - spin_unlock_irqrestore(&map->swap_lock, flags); - return ret; + return true; } int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift, @@ -80,7 +73,6 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift, for (i = 0; i < sb->map_nr; i++) { sb->map[i].depth = min(depth, bits_per_word); depth -= sb->map[i].depth; - spin_lock_init(&sb->map[i].swap_lock); } return 0; }