Hi Coly and Jens--
One concern I have with this is that it's going to wear out limited-lifetime SSDs a -lot- faster. Was any thought given to making this a tunable instead of just changing the behavior? Even if we have an anecdote or two that it seems to have increased performance for some workloads, I don't expect it will have increased performance in general and it may even be costly for some workloads (it all comes down to what is more useful in the cache-- somewhat-recently readahead data, or the data that it is displacing).
Regards,
Mike
On Thu, Jan 23, 2020 at 9:03 AM colyli@suse.de wrote:
From: Coly Li colyli@suse.de
In year 2007 high performance SSD was still expensive, in order to save more space for real workload or meta data, the readahead I/Os for non-meta data was bypassed and not cached on SSD.
In now days, SSD price drops a lot and people can find larger size SSD with more comfortable price. It is unncessary to bypass normal readahead I/Os to save SSD space for now.
This patch removes the code which checks REQ_RAHEAD tag of bio in check_should_bypass(), then all readahead I/Os will be cached on SSD.
NOTE: this patch still keeps the checking of "REQ_META|REQ_PRIO" in should_writeback(), because we still want to cache meta data I/Os even they are asynchronized.
Cc: stable@vger.kernel.org Signed-off-by: Coly Li colyli@suse.de Acked-by: Eric Wheeler bcache@linux.ewheeler.net
drivers/md/bcache/request.c | 9 --------- 1 file changed, 9 deletions(-)
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index 73478a91a342..acc07c4f27ae 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -378,15 +378,6 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio) op_is_write(bio_op(bio)))) goto skip;
/** Flag for bypass if the IO is for read-ahead or background,* unless the read-ahead request is for metadata* (eg, for gfs2 or xfs).*/if (bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND) &&!(bio->bi_opf & (REQ_META|REQ_PRIO)))goto skip;if (bio->bi_iter.bi_sector & (c->sb.block_size - 1) || bio_sectors(bio) & (c->sb.block_size - 1)) { pr_debug("skipping unaligned io");-- 2.16.4