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From: Ming Lei <ming.lei@redhat.com>
To: Wang Shanker <shankerwangmiao@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH 2/2] block: support bio merge for multi-range discard
Date: Wed, 9 Jun 2021 14:12:32 +0800	[thread overview]
Message-ID: <YMBb0E01P/nXq8fJ@T590> (raw)
In-Reply-To: <AAAB68D1-3F92-4F88-B192-2A202F7CE53D@gmail.com>

On Wed, Jun 09, 2021 at 11:05:59AM +0800, Wang Shanker wrote:
> 
> 
> > 2021年06月09日 08:45,Ming Lei <ming.lei@redhat.com> 写道:
> > 
> > So far multi-range discard treats each bio as one segment(range) of single
> > discard request. This way becomes not efficient if lots of small sized
> > discard bios are submitted, and one example is raid456.
> > 
> > Support bio merge for multi-range discard for improving lots of small
> > sized discard bios.
> > 
> > Turns out it is easy to support it:
> > 
> > 1) always try to merge bio first
> > 
> > 2) run into multi-range discard only if bio merge can't be done
> > 
> > 3) add rq_for_each_discard_range() for retrieving each range(segment)
> > of discard request
> > 
> > Reported-by: Wang Shanker <shankerwangmiao@gmail.com>
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> > block/blk-merge.c          | 12 ++++-----
> > drivers/block/virtio_blk.c |  9 ++++---
> > drivers/nvme/host/core.c   |  8 +++---
> > include/linux/blkdev.h     | 51 ++++++++++++++++++++++++++++++++++++++
> > 4 files changed, 66 insertions(+), 14 deletions(-)
> > 
> > diff --git a/block/blk-merge.c b/block/blk-merge.c
> > index bcdff1879c34..65210e9a8efa 100644
> > --- a/block/blk-merge.c
> > +++ b/block/blk-merge.c
> > @@ -724,10 +724,10 @@ static inline bool blk_discard_mergable(struct request *req)
> > static enum elv_merge blk_try_req_merge(struct request *req,
> > 					struct request *next)
> > {
> > -	if (blk_discard_mergable(req))
> > -		return ELEVATOR_DISCARD_MERGE;
> > -	else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
> > +	if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
> > 		return ELEVATOR_BACK_MERGE;
> > +	else if (blk_discard_mergable(req))
> 
> Shall we adjust how req->nr_phys_segments is calculated in 
> bio_attempt_discard_merge() so that multiple contiguous bio's can
> be seen as one segment?

I think it isn't necessary, because we try to merge discard IOs first
just like plain IO. So when bio_attempt_discard_merge() is reached, it
means that IOs can't be merged, so req->nr_phys_segments should be
increased by 1.


Thanks,
Ming


  reply	other threads:[~2021-06-09  6:12 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-09  0:45 [PATCH 0/2] block: discard merge fix & improvement Ming Lei
2021-06-09  0:45 ` [PATCH 1/2] block: fix discard request merge Ming Lei
2021-06-22  6:53   ` Christoph Hellwig
2021-06-22  7:51     ` Ming Lei
2021-06-09  0:45 ` [PATCH 2/2] block: support bio merge for multi-range discard Ming Lei
2021-06-09  3:05   ` Wang Shanker
2021-06-09  6:12     ` Ming Lei [this message]
2021-06-09  6:57       ` Wang Shanker
2021-06-22  6:55   ` Christoph Hellwig
2021-06-22  8:35     ` Miao Wang
2021-06-14 22:00 ` [PATCH 0/2] block: discard merge fix & improvement Ming Lei
2021-06-22  3:53   ` Ming Lei

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