Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754851AbdCJEgd (ORCPT ); Thu, 9 Mar 2017 23:36:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:40854 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751762AbdCJEgc (ORCPT ); Thu, 9 Mar 2017 23:36:32 -0500 From: NeilBrown To: Jens Axboe , Jack Wang Date: Fri, 10 Mar 2017 15:36:20 +1100 Cc: LKML , Lars Ellenberg , Kent Overstreet , Pavel Machek , Mike Snitzer , Mikulas Patocka , linux-raid@vger.kernel.org, device-mapper development , linux-block@vger.kernel.org Subject: [PATCH 4/5] blk: use non-rescuing bioset for q->bio_split. In-Reply-To: <87d1dphhuy.fsf@notabene.neil.brown.name> References: <87h93blz6g.fsf@notabene.neil.brown.name> <71562c2c-97f4-9a0a-32ec-30e0702ca575@profitbricks.com> <87lgsjj9w8.fsf@notabene.neil.brown.name> <87r328j00i.fsf@notabene.neil.brown.name> <87d1dphhuy.fsf@notabene.neil.brown.name> Message-ID: <871su5hhob.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2924 Lines: 78 --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable 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 and other bios allocated fro q->bio_split in the generic_make_request() queue. So no rescuing will ever be needed. Signed-off-by: NeilBrown =2D-- 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 c3992d17dc2c..375006c94c15 100644 =2D-- a/block/blk-core.c +++ b/block/blk-core.c @@ -714,7 +714,7 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_ma= sk, int node_id) if (q->id < 0) goto fail_q; =20 =2D q->bio_split =3D bioset_create_rescued(BIO_POOL_SIZE, 0); + q->bio_split =3D bioset_create(BIO_POOL_SIZE, 0); if (!q->bio_split) goto fail_id; =20 --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEG8Yp69OQ2HB7X0l6Oeye3VZigbkFAljCLUQACgkQOeye3VZi gbmtbw//Vqna/c1XoVNNyGIbpl7CVQfYE1gHgFUo/NG9BuGrZw7iF2NRUhTr3BzS 7vNIgMsj5feegCG6d4yKS6LGck6sYNWu62yWvjG+DuaK9PhGL7yt5xZyyxDe42y9 2HUkQVpg8XT2UgxhpTpEHYp2TQTkz6QebGchdeU6ExmUr1hLoPi/DXAiLr48H9NQ bHii/ukL5BymRm9cydsEPOuHLAWndZgWNQwOq2k87AT7kXobWzEpLdoNtLZpMHc+ aPMpAyYg6+rZRxn4WOuCvkeYlwIB8WeWWOlqolsCzSriY+974lwGv2IOSN7MxEtV v/Mlm/z1AHbbeNwfE6hHM5KoaemWV/gGx2zATGBiNUBV3jawkBdWhExcmvqkt+bt A+Fac/jOKee0WuLiFwU24sB4v128KKrXUrlNvpDGZIjhbQ3uIGDBV3zeVwPrMZhh 8hHCfs8NiiSR2u19xbeiIwHtbrW2QtFvAPbv/RmvFZMgWammMUVUTByMHoPfjLcR YhQwooNnTj7Q/qorLRtxLT2Ut0ZRXBhXJIt3Bcrvq1M3lN+UQLXVDQ7s4YsKzhZL baATDHgykZ0jl+6dh62YSQJw8ij3O/tmme+z6bn/o3UBWujPGN8CRSkgeQogWcaX MOre5eE4IFu0Vlk1vG0K/5wxQpmzMldpglKXOo+0z28BMsgTaXQ= =taSq -----END PGP SIGNATURE----- --=-=-=--