* [PATCH] sbitmap: Consider cleared bits in sbitmap_bitmap_show()
@ 2020-07-01 8:06 John Garry
2020-07-01 16:53 ` Jens Axboe
0 siblings, 1 reply; 2+ messages in thread
From: John Garry @ 2020-07-01 8:06 UTC (permalink / raw)
To: axboe; +Cc: bvanassche, osandov, linux-block, linux-kernel, hare, John Garry
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@huawei.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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] sbitmap: Consider cleared bits in sbitmap_bitmap_show()
2020-07-01 8:06 [PATCH] sbitmap: Consider cleared bits in sbitmap_bitmap_show() John Garry
@ 2020-07-01 16:53 ` Jens Axboe
0 siblings, 0 replies; 2+ messages in thread
From: Jens Axboe @ 2020-07-01 16:53 UTC (permalink / raw)
To: John Garry; +Cc: bvanassche, osandov, linux-block, linux-kernel, hare
On 7/1/20 2:06 AM, John Garry wrote:
> 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.
Applied, thanks.
--
Jens Axboe
^ permalink raw reply [flat|nested] 2+ messages in thread
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