On Mon, May 4, 2015 at 12:47 AM, Ming Lin <mlin@xxxxxxxxxx> wrote:
> 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?
Hi NeilBrown,
Are you OK with below fix?
Then I'll include it in the next version.
Thanks.
>
> 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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