From: Ming Lei <ming.lei@redhat.com>
To: NeilBrown <neilb@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Ming Lei <tom.leiming@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 04/13] blk: use non-rescuing bioset for q->bio_split.
Date: Tue, 2 May 2017 19:54:20 +0800 [thread overview]
Message-ID: <20170502115419.GD1803@ming.t460p> (raw)
In-Reply-To: <149369654452.5146.12018336836086489178.stgit@noble>
On Tue, May 02, 2017 at 01:42:24PM +1000, NeilBrown wrote:
> A rescuing bioset is only useful if there might be bios from
> that same bioset on the bio_list_on_stack queue at a time
> when bio_alloc_bioset() is called. This never applies to
> q->bio_split.
>
> Allocations from q->bio_split are only ever made from
> blk_queue_split() which is only ever called early in each of
> various make_request_fn()s. The original bio (call this A)
> is then passed to generic_make_request() and is placed on
> the bio_list_on_stack queue, and the bio that was allocated
> from q->bio_split (B) is processed.
>
> The processing of this may cause other bios to be passed to
> generic_make_request() or may even cause the bio B itself to
> be passed, possible after some prefix has been split off
> (using some other bioset).
>
> generic_make_request() now guarantees that all of these bios
> (B and dependants) will be fully processed before the tail
> of the original bio A gets handled. None of these early bios
> can possible trigger an allocation from the original
> q->bio_split as they are either too small to require
> splitting or (more likely) are destined for a different queue.
>
> The next time that the original q->bio_split might be used
> by this thread is when A is processed again, as it might
> still be too big to handle directly. By this time there
> cannot be any other bios allocated from q->bio_split in the
> generic_make_request() queue. So no rescuing will ever be
> needed.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: NeilBrown <neilb@suse.com>
> ---
> block/blk-core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ae51f159a2ca..3797753f4085 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -730,7 +730,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
> if (q->id < 0)
> goto fail_q;
>
> - q->bio_split = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS | BIOSET_NEED_RESCUER);
> + q->bio_split = bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
> if (!q->bio_split)
> goto fail_id;
>
>
>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Thanks,
Ming
next prev parent reply other threads:[~2017-05-02 11:54 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-02 3:42 [PATCH 00/13] block: assorted cleanup for bio splitting and cloning NeilBrown
2017-05-02 3:42 ` [PATCH 03/13] blk: make the bioset rescue_workqueue optional NeilBrown
2017-05-02 8:14 ` Christoph Hellwig
2017-05-02 11:00 ` Ming Lei
2017-05-02 22:10 ` NeilBrown
2017-05-02 22:34 ` [PATCH 03/13 V2] " NeilBrown
2017-05-03 3:24 ` Ming Lei
2017-05-02 3:42 ` [PATCH 02/13] blk: replace bioset_create_nobvec() with a flags arg to bioset_create() NeilBrown
2017-05-02 8:06 ` Christoph Hellwig
2017-05-02 21:47 ` NeilBrown
2017-05-02 9:40 ` Ming Lei
2017-05-02 3:42 ` [PATCH 01/13] blk: remove bio_set arg from blk_queue_split() NeilBrown
2017-05-02 10:44 ` javigon
2017-05-02 3:42 ` [PATCH 05/13] block: Improvements to bounce-buffer handling NeilBrown
2017-05-02 8:13 ` Christoph Hellwig
2017-05-02 11:56 ` Ming Lei
2017-05-02 3:42 ` [PATCH 04/13] blk: use non-rescuing bioset for q->bio_split NeilBrown
2017-05-02 11:54 ` Ming Lei [this message]
2017-05-02 23:21 ` [PATCH 04/13 V2] " NeilBrown
2017-05-02 3:42 ` [PATCH 09/13] lightnvm/pblk-read: use bio_clone_fast() NeilBrown
2017-05-02 8:15 ` Christoph Hellwig
2017-05-02 11:22 ` Javier González
2017-05-02 21:51 ` NeilBrown
2017-05-03 6:42 ` Javier González
2017-05-02 3:42 ` [PATCH 10/13] xen-blkfront: remove bio splitting NeilBrown
2017-05-02 8:15 ` Christoph Hellwig
2017-05-02 3:42 ` [PATCH 07/13] drbd: use bio_clone_fast() instead of bio_clone() NeilBrown
2017-05-02 23:20 ` [PATCH 07/13 V2] " NeilBrown
2017-05-02 3:42 ` [PATCH 06/13] rbd: " NeilBrown
2017-05-02 3:42 ` [PATCH 08/13] pktcdvd: " NeilBrown
2017-05-02 3:42 ` [PATCH 13/13] block: don't check for BIO_MAX_PAGES in blk_bio_segment_split() NeilBrown
2017-05-02 8:15 ` Christoph Hellwig
2017-05-02 10:22 ` Ming Lei
2017-05-02 22:54 ` NeilBrown
2017-05-02 23:50 ` Ming Lei
2017-05-02 3:42 ` [PATCH 11/13] bcache: use kmalloc to allocate bio in bch_data_verify() NeilBrown
2017-05-02 3:42 ` [PATCH 12/13] block: remove bio_clone() and all references NeilBrown
2017-05-11 0:58 ` [PATCH 00/13] block: assorted cleanup for bio splitting and cloning NeilBrown
2017-06-16 5:54 ` NeilBrown
2017-06-16 6:42 ` Christoph Hellwig
2017-06-16 7:30 ` NeilBrown
2017-06-16 7:34 ` Christoph Hellwig
2017-06-16 20:45 ` Jens Axboe
2017-06-18 4:40 ` NeilBrown
2017-06-18 4:40 ` NeilBrown
2017-06-18 4:38 NeilBrown
2017-06-18 4:38 ` [PATCH 04/13] blk: use non-rescuing bioset for q->bio_split NeilBrown
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