From patchwork Fri Mar 10 06:00:47 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 9615089 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 D903460414 for ; Fri, 10 Mar 2017 06:03:03 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C9C7C286C0 for ; Fri, 10 Mar 2017 06:03:03 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BAEF9286E7; Fri, 10 Mar 2017 06:03:03 +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=unavailable 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 6C004286C0 for ; Fri, 10 Mar 2017 06:03:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932077AbdCJGCs (ORCPT ); Fri, 10 Mar 2017 01:02:48 -0500 Received: from mx2.suse.de ([195.135.220.15]:44022 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755010AbdCJGCd (ORCPT ); Fri, 10 Mar 2017 01:02:33 -0500 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 mx2.suse.de (Postfix) with ESMTP id 2217CAAB4; Fri, 10 Mar 2017 06:02:21 +0000 (UTC) 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> User-Agent: StGit/0.17.1-dirty 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. 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;