linux-kernel - [PATCH 1/4] sbitmap: remove unnecessary calculation of alloc_hint in __sbitmap_get

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Message-Id: <20221208220147.3315388-2-shikemeng@huaweicloud.com>
Date:   Fri,  9 Dec 2022 06:01:44 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linfeilong@...wei.com, liuzhiqiang26@...wei.com
Subject: [PATCH 1/4] sbitmap: remove unnecessary calculation of alloc_hint in __sbitmap_get_shallow

We calculate allow_hint in next word as following:

/* low sb->shift bit of alloc_hint will be 0 after this shift */
alloc_hint = index << sb->shift;

/* get low sb->shift bit of alloc_hit */
SB_NR_TO_BIT(sb, alloc_hint)

So alloc_hit in next word will always be zero. Simpfy alloc_hit calculation
in __sbitmap_get_shallow according to the alloc_hit calculation in
__sbitmap_get.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 lib/sbitmap.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 586deb333237..cb5e03a2d65b 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -243,6 +243,7 @@ static int __sbitmap_get_shallow(struct sbitmap *sb,
 	int nr = -1;
 
 	index = SB_NR_TO_INDEX(sb, alloc_hint);
+	alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
 
 	for (i = 0; i < sb->map_nr; i++) {
 again:
@@ -250,7 +251,7 @@ static int __sbitmap_get_shallow(struct sbitmap *sb,
 					min_t(unsigned int,
 					      __map_depth(sb, index),
 					      shallow_depth),
-					SB_NR_TO_BIT(sb, alloc_hint), true);
+					alloc_hint, true);
 		if (nr != -1) {
 			nr += index << sb->shift;
 			break;
@@ -260,13 +261,9 @@ static int __sbitmap_get_shallow(struct sbitmap *sb,
 			goto again;
 
 		/* Jump to next index. */
-		index++;
-		alloc_hint = index << sb->shift;
-
-		if (index >= sb->map_nr) {
+		alloc_hint = 0;
+		if (++index >= sb->map_nr)
 			index = 0;
-			alloc_hint = 0;
-		}
 	}
 
 	return nr;
-- 
2.30.0