Re: [PATCH v5 10/11] block: remove bio_get_nr_vecs()

From: Steven Whitehouse
Date: Mon Jul 06 2015 - 06:58:45 EST


Hi,


On 06/07/15 08:44, Ming Lin wrote:
From: Kent Overstreet <kent.overstreet@xxxxxxxxx>

We can always fill up the bio now, no need to estimate the possible
size based on queue parameters.
[snip]
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 2c1ae86..64d3116 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -261,18 +261,11 @@ void gfs2_log_flush_bio(struct gfs2_sbd *sdp, int rw)
static struct bio *gfs2_log_alloc_bio(struct gfs2_sbd *sdp, u64 blkno)
{
struct super_block *sb = sdp->sd_vfs;
- unsigned nrvecs = bio_get_nr_vecs(sb->s_bdev);
struct bio *bio;
BUG_ON(sdp->sd_log_bio);
- while (1) {
- bio = bio_alloc(GFP_NOIO, nrvecs);
- if (likely(bio))
- break;
- nrvecs = max(nrvecs/2, 1U);
- }
-
+ bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES);
bio->bi_iter.bi_sector = blkno * (sb->s_blocksize >> 9);
bio->bi_bdev = sb->s_bdev;
bio->bi_end_io = gfs2_end_log_write;

When I wrote this loop I understood that bio_alloc(GFP_NOIO, x) was only guaranteed to be successful in the case x = 1, and that for x > 1, it might return NULL. Does this now mean that for x = BIO_MAX_PAGES it will be guaranteed to never return NULL in this case?

Steve.

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