From mboxrd@z Thu Jan 1 00:00:00 1970 From: NeilBrown Subject: [PATCH 4/5] blk: use non-rescuing bioset for q->bio_split. Date: Fri, 10 Mar 2017 17:00:47 +1100 Message-ID: <148912564749.4002.12977222491155249514.stgit@noble> References: <148912539296.4002.219258660543808741.stgit@noble> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <148912539296.4002.219258660543808741.stgit@noble> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Jens Axboe Cc: linux-raid@vger.kernel.org, Mike Snitzer , LKML , linux-block@vger.kernel.org, device-mapper development , Mikulas Patocka , Pavel Machek , Jack Wang , Lars Ellenberg , Kent Overstreet List-Id: linux-raid.ids 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. Signed-off-by: NeilBrown --- 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 430c82f646eb..fae7966e1f98 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -712,7 +712,7 @@ 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_rescued(BIO_POOL_SIZE, 0); + q->bio_split = bioset_create(BIO_POOL_SIZE, 0); if (!q->bio_split) goto fail_id; From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: NeilBrown To: Jens Axboe Date: Fri, 10 Mar 2017 17:00:47 +1100 Subject: [PATCH 4/5] blk: use non-rescuing bioset for q->bio_split. Cc: linux-block@vger.kernel.org, Mike Snitzer , LKML , linux-raid@vger.kernel.org, device-mapper development , Mikulas Patocka , Pavel Machek , Jack Wang , Lars Ellenberg , Kent Overstreet Message-ID: <148912564749.4002.12977222491155249514.stgit@noble> In-Reply-To: <148912539296.4002.219258660543808741.stgit@noble> References: <148912539296.4002.219258660543808741.stgit@noble> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" List-ID: 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. Signed-off-by: NeilBrown --- 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 430c82f646eb..fae7966e1f98 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -712,7 +712,7 @@ 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_rescued(BIO_POOL_SIZE, 0); + q->bio_split = bioset_create(BIO_POOL_SIZE, 0); if (!q->bio_split) goto fail_id;