linux-kernel - [PATCH] sbitmap: Consider cleared bits in sbitmap_bitmap

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Date:   Wed, 1 Jul 2020 16:06:25 +0800
From:   John Garry <john.garry@...wei.com>
To:     <axboe@...nel.dk>
CC:     <bvanassche@....org>, <osandov@...com>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <hare@...e.com>, John Garry <john.garry@...wei.com>
Subject: [PATCH] sbitmap: Consider cleared bits in sbitmap_bitmap_show()

sbitmap works by maintaining separate bitmaps of set and cleared bits.
The set bits are cleared in a batch, to save the burden of continuously
locking the "word" map to unset.

sbitmap_bitmap_show() only shows the set bits (in "word"), which is not
too much use, so mask out the cleared bits.

Fixes: ea86ea2cdced ("sbitmap: ammortize cost of clearing bits")
Signed-off-by: John Garry <john.garry@...wei.com>

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index af88d1346dd7..267aa7709416 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -292,8 +292,11 @@ void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
 
 	for (i = 0; i < sb->map_nr; i++) {
 		unsigned long word = READ_ONCE(sb->map[i].word);
+		unsigned long cleared = READ_ONCE(sb->map[i].cleared);
 		unsigned int word_bits = READ_ONCE(sb->map[i].depth);
 
+		word &= ~cleared;
+
 		while (word_bits > 0) {
 			unsigned int bits = min(8 - byte_bits, word_bits);
 
-- 
2.26.2