On 04/28/2015 03:09 PM, NeilBrown wrote:
> On Mon, 27 Apr 2015 23:48:34 -0700 Ming Lin <mlin@xxxxxxxxxx> wrote:
>
>> From: Kent Overstreet <kent.overstreet@xxxxxxxxx>
>>
>> As generic_make_request() is now able to handle arbitrarily sized bios,
>> it's no longer necessary for each individual block driver to define its
>> own ->merge_bvec_fn() callback. Remove every invocation completely.
>
> This patch it just a little premature I think.
>
> md/raid5 still assumes read requests will mostly fit within a single chunk
> (which merge_bvec_fn encourages) so they can be serviced without using the
> stripe-cache.
> You've just broken that assumption.
>
> I think 'chunk_aligned_read' needs to get a loop using bio_split, a bit like
> raid0, first.
How about below?
drivers/md/raid5.c | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e42b624..2ddfa1e 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -4709,7 +4709,7 @@ static void raid5_align_endio(struct bio *bi, int error)
add_bio_to_retry(raid_bi, conf);
}
-static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
+static int __chunk_aligned_read(struct mddev *mddev, struct bio *raid_bio)
{
struct r5conf *conf = mddev->private;
int dd_idx;
@@ -4718,7 +4718,7 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
sector_t end_sector;
if (!in_chunk_boundary(mddev, raid_bio)) {
- pr_debug("chunk_aligned_read : non aligned\n");
+ pr_debug("__chunk_aligned_read : non aligned\n");
return 0;
}
/*
@@ -4793,6 +4793,35 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
}
}
+static struct bio *chunk_aligned_read(struct mddev *mddev, struct bio *raid_bio)
+{
+ struct bio *split;
+
+ do {
+ sector_t sector = raid_bio->bi_iter.bi_sector;
+ unsigned chunk_sects = mddev->chunk_sectors;
+
+ unsigned sectors = chunk_sects -
+ (likely(is_power_of_2(chunk_sects))
+ ? (sector & (chunk_sects-1))
+ : sector_div(sector, chunk_sects));
+
+ if (sectors < bio_sectors(raid_bio)) {
+ split = bio_split(raid_bio, sectors, GFP_NOIO, fs_bio_set);
+ bio_chain(split, raid_bio);
+ } else
+ split = raid_bio;
+
+ if (!__chunk_aligned_read(mddev, split)) {
+ if (split != raid_bio)
+ generic_make_request(raid_bio);
+ return split;
+ }
+ } while (split != raid_bio);
+
+ return NULL;
+}
+
/* __get_priority_stripe - get the next stripe to process
*
* Full stripe writes are allowed to pass preread active stripes up until
@@ -5071,7 +5100,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
*/
if (rw == READ && mddev->degraded == 0 &&
mddev->reshape_position == MaxSector &&
- chunk_aligned_read(mddev,bi))
+ (!(bi = chunk_aligned_read(mddev, bi))))
return;
if (unlikely(bi->bi_rw & REQ_DISCARD)) {
--
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