On 9/26/18 12:32 AM, Adam Manzanares wrote:
On 9/25/18 9:12 AM, Coly Li wrote:
In cached_dev_cache_miss() and check_should_bypass(), REQ_META is used
to check whether a bio is for metadata request. REQ_META is used for
blktrace, the correct REQ_ flag should be REQ_PRIO. This flag means the
bio should be prior to other bio, and frequently be used to indicate
metadata io in file system code.
This patch replaces REQ_META with correct flag REQ_PRIO.
CC Adam Manzanares because he explains to me what REQ_PRIO is for.
Sorry for the confusion, I was talking about using the bi_ioprio field
to pass ioprio information down to devices that support prioritized
commands. I haven't used the REQ_PRIO flag in the work that I have done.
Hi Adam,
Aha, I misunderstood you. After 'git blame' I realize REQ_PRIO is
invented by Christoph Hellwig,
Add a new REQ_PRIO to let requests preempt others in the cfq I/O
schedule,
and lave REQ_META purely for marking requests as metadata in blktrace.
From log of commit 65299a3b788b ("block: separate priority boosting
from REQ_META") it seems this patch still uses REQ_PRIO in a correct
way. And, thank you for clarifying this :-)
Coly Li
Signed-off-by: Coly Li <colyli@xxxxxxx>
Cc: Adam Manzanares <adam.manzanares@xxxxxxx>
---
drivers/md/bcache/request.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 51be355a3309..13d3355a90c0 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -395,7 +395,7 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
* unless the read-ahead request is for metadata (eg, for gfs2).
*/
if (bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND) &&
- !(bio->bi_opf & REQ_META))
+ !(bio->bi_opf & REQ_PRIO))
goto skip;
if (bio->bi_iter.bi_sector & (c->sb.block_size - 1) ||
@@ -877,7 +877,7 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s,
}
if (!(bio->bi_opf & REQ_RAHEAD) &&
- !(bio->bi_opf & REQ_META) &&
+ !(bio->bi_opf & REQ_PRIO) &&
s->iop.c->gc_stats.in_use < CUTOFF_CACHE_READA)
reada = min_t(sector_t, dc->readahead >> 9,
get_capacity(bio->bi_disk) - bio_end_sector(bio));
