Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965420AbdDTFpZ (ORCPT ); Thu, 20 Apr 2017 01:45:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:40371 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965008AbdDTFpN (ORCPT ); Thu, 20 Apr 2017 01:45:13 -0400 From: NeilBrown To: Jens Axboe Date: Thu, 20 Apr 2017 15:38:49 +1000 Subject: [PATCH 03/11] blk: use non-rescuing bioset for q->bio_split. Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <149266672879.27388.10034843544514097987.stgit@noble> In-Reply-To: <149266645258.27388.14083229348123176454.stgit@noble> References: <149266645258.27388.14083229348123176454.stgit@noble> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1914 Lines: 50 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 23f20cb84b2f..f5d64ad75b36 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -728,7 +728,7 @@ 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;