| Message ID | 20171129071115.7399-2-anand.jain@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index b93fe05a39c7..9a539cf82e51 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8014,9 +8014,6 @@ static blk_status_t dio_read_error(struct inode *inode, struct bio *failed_bio, } segs = bio_segments(failed_bio); - if (segs > 1 || - (failed_bio->bi_io_vec->bv_len > btrfs_inode_sectorsize(inode))) - read_mode |= REQ_FAILFAST_DEV; isector = start - btrfs_io_bio(failed_bio)->logical; isector >>= inode->i_sb->s_blocksize_bits;
Similarly do not set the REQ_FAILFAST_DEV for mirror read bio during dio. [Taken from patch in ml btrfs: submit a normal bio for the mirror read] [When the fist mirror failed to read we submit bio again to read from the 2nd mirror, however during this, we also set the flag REQ_FAILFAST_DEV which indicates to the underlying block device driver not to perform the default IO retry (sd, 5 counts), and thus command will be failed and returned at the first failed attempt. On the contrary, in fact, it should have been other way around that is, as 2nd mirror being the last copy of the data, it should rather try equally hard to make this read cmd successful and at the same time with or without REQ_FAILFAST_DEV there is no performance benefits if the command is successful in the first attempt itself. The only benefit which would be achieved with REQ_FAILFAST_DEV is that when both the copies encounter failed read, then for the applications, the EIO will be reported roughly 40% faster (since it saves 4 retries). But when first mirror has failed whats more important will be to make a successful read from the 2nd mirror. And for the DUP case where both the copies are on the same disk, this makes to retry 5 times on 2 different LBA/sector but on the same disk, which probably is not a good idea if your test case involves pulling out the disk. But as of now we don't have a way to tell the block layer how critical a read is, so that block layer can accommodate the retry dynamically]. Signed-off-by: Anand Jain <anand.jain@oracle.com> --- fs/btrfs/inode.c | 3 --- 1 file changed, 3 deletions(-)