From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 32DD0C433ED for ; Tue, 6 Apr 2021 07:32:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB3C8613C0 for ; Tue, 6 Apr 2021 07:32:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233688AbhDFHci (ORCPT ); Tue, 6 Apr 2021 03:32:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:52282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234701AbhDFHch (ORCPT ); Tue, 6 Apr 2021 03:32:37 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id EFB0A60C41; Tue, 6 Apr 2021 07:32:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1617694350; bh=utzK9JJnm7CSmXkantZvzPx3+Nb6tDzqIuRCbQBb+V4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=psPtI1AxNwNSukh8NKwheQgd0WDmruwl+bGW1gxcA6cX+QSrLvaMRY1+KbZ/FNDdo 8J1qjYsV2IIUFD6m3DKKkPCKYrfPrq/u8Y/mOI20pA4DTmhHyjcIgPcigAlyI6xruu 5HFiK7u0jui2dfxxrevvQfu+te2lm7n2JIE5/H/w= Date: Tue, 6 Apr 2021 09:32:24 +0200 From: Greg KH To: Changheun Lee Cc: Johannes.Thumshirn@wdc.com, asml.silence@gmail.com, axboe@kernel.dk, damien.lemoal@wdc.com, hch@infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ming.lei@redhat.com, osandov@fb.com, patchwork-bot@kernel.org, tj@kernel.org, tom.leiming@gmail.com, jisoo2146.oh@samsung.com, junho89.kim@samsung.com, mj0123.lee@samsung.com, seunghwan.hyun@samsung.com, sookwan7.kim@samsung.com, woosung2.lee@samsung.com, yt0928.kim@samsung.com Subject: Re: [RESEND PATCH v5 1/2] bio: limit bio max size Message-ID: References: <20210316074401.4594-1-nanich.lee@samsung.com> <20210406013128.16284-1-nanich.lee@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210406013128.16284-1-nanich.lee@samsung.com> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Apr 06, 2021 at 10:31:28AM +0900, Changheun Lee wrote: > > bio size can grow up to 4GB when muli-page bvec is enabled. > > but sometimes it would lead to inefficient behaviors. > > in case of large chunk direct I/O, - 32MB chunk read in user space - > > all pages for 32MB would be merged to a bio structure if the pages > > physical addresses are contiguous. it makes some delay to submit > > until merge complete. bio max size should be limited to a proper size. > > > > When 32MB chunk read with direct I/O option is coming from userspace, > > kernel behavior is below now in do_direct_IO() loop. it's timeline. > > > > | bio merge for 32MB. total 8,192 pages are merged. > > | total elapsed time is over 2ms. > > |------------------ ... ----------------------->| > > | 8,192 pages merged a bio. > > | at this time, first bio submit is done. > > | 1 bio is split to 32 read request and issue. > > |---------------> > > |---------------> > > |---------------> > > ...... > > |---------------> > > |--------------->| > > total 19ms elapsed to complete 32MB read done from device. | > > > > If bio max size is limited with 1MB, behavior is changed below. > > > > | bio merge for 1MB. 256 pages are merged for each bio. > > | total 32 bio will be made. > > | total elapsed time is over 2ms. it's same. > > | but, first bio submit timing is fast. about 100us. > > |--->|--->|--->|---> ... -->|--->|--->|--->|--->| > > | 256 pages merged a bio. > > | at this time, first bio submit is done. > > | and 1 read request is issued for 1 bio. > > |---------------> > > |---------------> > > |---------------> > > ...... > > |---------------> > > |--------------->| > > total 17ms elapsed to complete 32MB read done from device. | > > > > As a result, read request issue timing is faster if bio max size is limited. > > Current kernel behavior with multipage bvec, super large bio can be created. > > And it lead to delay first I/O request issue. > > > > Signed-off-by: Changheun Lee > > --- > > block/bio.c | 13 ++++++++++++- > > include/linux/bio.h | 2 +- > > include/linux/blkdev.h | 3 +++ > > 3 files changed, 16 insertions(+), 2 deletions(-) > > > > diff --git a/block/bio.c b/block/bio.c > > index 1f2cc1fbe283..c528e1f944c7 100644 > > --- a/block/bio.c > > +++ b/block/bio.c > > @@ -287,6 +287,17 @@ void bio_init(struct bio *bio, struct bio_vec *table, > > } > > EXPORT_SYMBOL(bio_init); > > > > +unsigned int bio_max_size(struct bio *bio) > > +{ > > + struct request_queue *q = bio->bi_disk->queue; > > + > > + if (blk_queue_limit_bio_size(q)) > > + return blk_queue_get_max_sectors(q, bio_op(bio)) > > + << SECTOR_SHIFT; > > + > > + return UINT_MAX; > > +} > > + > > /** > > * bio_reset - reinitialize a bio > > * @bio: bio to reset > > @@ -877,7 +888,7 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page, > > struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1]; > > > > if (page_is_mergeable(bv, page, len, off, same_page)) { > > - if (bio->bi_iter.bi_size > UINT_MAX - len) { > > + if (bio->bi_iter.bi_size > bio_max_size(bio) - len) { > > *same_page = false; > > return false; > > } > > diff --git a/include/linux/bio.h b/include/linux/bio.h > > index 1edda614f7ce..13b6f6562a5b 100644 > > --- a/include/linux/bio.h > > +++ b/include/linux/bio.h > > @@ -113,7 +113,7 @@ static inline bool bio_full(struct bio *bio, unsigned len) > > if (bio->bi_vcnt >= bio->bi_max_vecs) > > return true; > > > > - if (bio->bi_iter.bi_size > UINT_MAX - len) > > + if (bio->bi_iter.bi_size > bio_max_size(bio) - len) > > return true; > > > > return false; > > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > > index f94ee3089e01..3aeab9e7e97b 100644 > > --- a/include/linux/blkdev.h > > +++ b/include/linux/blkdev.h > > @@ -621,6 +621,7 @@ struct request_queue { > > #define QUEUE_FLAG_RQ_ALLOC_TIME 27 /* record rq->alloc_time_ns */ > > #define QUEUE_FLAG_HCTX_ACTIVE 28 /* at least one blk-mq hctx is active */ > > #define QUEUE_FLAG_NOWAIT 29 /* device supports NOWAIT */ > > +#define QUEUE_FLAG_LIMIT_BIO_SIZE 30 /* limit bio size */ > > > > #define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \ > > (1 << QUEUE_FLAG_SAME_COMP) | \ > > @@ -667,6 +668,8 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q); > > #define blk_queue_fua(q) test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags) > > #define blk_queue_registered(q) test_bit(QUEUE_FLAG_REGISTERED, &(q)->queue_flags) > > #define blk_queue_nowait(q) test_bit(QUEUE_FLAG_NOWAIT, &(q)->queue_flags) > > +#define blk_queue_limit_bio_size(q) \ > > + test_bit(QUEUE_FLAG_LIMIT_BIO_SIZE, &(q)->queue_flags) > > > > extern void blk_set_pm_only(struct request_queue *q); > > extern void blk_clear_pm_only(struct request_queue *q); > > -- > > 2.28.0 > > > > Please feedback to me if more modification is needed to apply. :) You are adding code that tests for a value to be set, yet you never set it in this code so why is it needed at all? thanks, greg k-h