From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" List-ID: --=-=-= 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 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 =2D-- 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 =2D-- a/block/blk-core.c +++ b/block/blk-core.c @@ -730,8 +730,7 @@ 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(BIO_POOL_SIZE, 0, (BIOSET_NEED_BVECS | =2D BIOSET_NEED_RESCUER)); + q->bio_split =3D bioset_create(BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS); if (!q->bio_split) goto fail_id; =20 =2D-=20 2.12.2 --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEG8Yp69OQ2HB7X0l6Oeye3VZigbkFAlkJFI0ACgkQOeye3VZi gbmVihAAqsd8Ax/uFAsgLXv6/vfT/4gzWIfocbDCwhReHtNzTrgSAGUKD9bbiDCg Kmc10unaw1Wvk0tZ54wPuF+4hWvBRSI8pECjgaC8Ez7DmhFxPkUa7mcAqpddaOH1 wMMUbipK8Fm7EE36dVSzd6klxEicqllQExZE2WP/NN8gl3i2WvINkhNJMo9MmcOU MGh08NKtfZF2Xr6nDuLieCBVIHonJ9AY4ky+JgNFRTs3U1Rh+VGQH9lDloDk7qJ4 VXKk31pSzB5dj8mLLCVrriTahXhlW2n7NkLRp707BbkO6zs8rKTrCyCga9uVl9tE AgOjBlqCHOc+m/ep9ZUPg/o4R8XzdcBPY6+2kcVhrjTVOpWavo+Txb6yaPpn7Z/C uLK1EbKf0vNho05Yt+vYe4ZYgF+BRsHgssa7b+dvdbpzWS54KXhZCF1xTV/X9Ni2 SmncTZSYJSaPl4de2ZhoMN1ylJOJCgtcU16SUf/Z4Jj/8+xFVIv4rJOJEB9oNZ8o 59XXf51eN1luSyV//fKcBowr0+OUSrekrg6pHP9WcMX6uwFPUxftRjspyNQ6bCLU 7R/n0KeiLceW2+rI3ElRY3FSkRjDblvTymZEe/RsLLl9MNfwDhu2QDwBduvworzV IyE6VzPvC19DHLlsQUSJB+jS1+B5d+nKKtn28TEH7X5fgFUSOEI= =m538 -----END PGP SIGNATURE----- --=-=-=--