From patchwork Tue May 2 23:21:48 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 9708647 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 5C19060349 for ; Tue, 2 May 2017 23:21:58 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4D0D4285EB for ; Tue, 2 May 2017 23:21:58 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3FA83285F0; Tue, 2 May 2017 23:21:58 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B88BE285EB for ; Tue, 2 May 2017 23:21:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750819AbdEBXV4 (ORCPT ); Tue, 2 May 2017 19:21:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:60261 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750773AbdEBXV4 (ORCPT ); Tue, 2 May 2017 19:21:56 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C557AAAB2; Tue, 2 May 2017 23:21:54 +0000 (UTC) From: NeilBrown To: Jens Axboe Date: Wed, 03 May 2017 09:21:48 +1000 Cc: linux-block@vger.kernel.org, Ming Lei , linux-kernel@vger.kernel.org Subject: [PATCH 04/13 V2] blk: use non-rescuing bioset for q->bio_split. In-Reply-To: <149369654452.5146.12018336836086489178.stgit@noble> References: <149369628671.5146.4865312503373040039.stgit@noble> <149369654452.5146.12018336836086489178.stgit@noble> Message-ID: <87o9vaq1yr.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 Reviewed-by: Ming Lei Signed-off-by: NeilBrown --- This patch needed to be refreshed after previous patch had long lines wrapped. Also added Ming's Reviewed-by. Thanks, NeilBrown block/blk-core.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index bc66cd595bef..3797753f4085 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -730,8 +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;