2020-07-01 08:10:49

by John Garry

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 <[email protected]>

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

2020-07-01 16:54:45

by Jens Axboe

Subject: Re: [PATCH] sbitmap: Consider cleared bits in sbitmap_bitmap_show()

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