linux-kernel - [PATCH 3/6] sbitmap: don't loop twice in find_next_zero

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Message-ID: <20230720094555.1397621-4-chengming.zhou@linux.dev>
Date:   Thu, 20 Jul 2023 17:45:52 +0800
From:   chengming.zhou@...ux.dev
To:     axboe@...nel.dk, osandov@...com, ming.lei@...hat.com,
        kbusch@...nel.org, krisman@...e.de
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        zhouchengming@...edance.com
Subject: [PATCH 3/6] sbitmap: don't loop twice in find_next_zero_bit()

From: Chengming Zhou <zhouchengming@...edance.com>

__sbitmap_get_shallow() try to allocate a free bit with a limited depth,
which always wrap when finding a free bit in the word, even in the
round-robin case. So it seems we don't need strict round-robin here.

This way will loop twice in find_next_zero_bit() in the word, no point
in looping twice in find_next_zero_bit() if we don't want strict
round-robin for this case.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 lib/sbitmap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index ccb96d1f92ba..0f3943bd3940 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -268,7 +268,9 @@ static int __sbitmap_get_shallow(struct sbitmap *sb,
 	unsigned int index;
 
 	index = SB_NR_TO_INDEX(sb, alloc_hint);
-	alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
+
+	/* No point in looping twice in find_next_zero_bit() for this case. */
+	alloc_hint = 0;
 
 	return sbitmap_find_bit(sb, shallow_depth, index, alloc_hint, true);
 }
-- 
2.41.0