From: Greg KH <gregkh@linuxfoundation.org>
To: Changheun Lee <nanich.lee@samsung.com>
Cc: Johannes.Thumshirn@wdc.com, asml.silence@gmail.com,
axboe@kernel.dk, damien.lemoal@wdc.com, hch@infradead.org,
jisoo2146.oh@samsung.com, junho89.kim@samsung.com,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
ming.lei@redhat.com, mj0123.lee@samsung.com, osandov@fb.com,
patchwork-bot@kernel.org, seunghwan.hyun@samsung.com,
sookwan7.kim@samsung.com, tj@kernel.org, tom.leiming@gmail.com,
woosung2.lee@samsung.com, yt0928.kim@samsung.com
Subject: Re: [RESEND PATCH v5 1/2] bio: limit bio max size
Date: Wed, 7 Apr 2021 09:40:59 +0200 [thread overview]
Message-ID: <YG1iC944hUkBniDM@kroah.com> (raw)
In-Reply-To: <20210407065507.6240-1-nanich.lee@samsung.com>
On Wed, Apr 07, 2021 at 03:55:07PM +0900, Changheun Lee wrote:
> > On Wed, Apr 07, 2021 at 02:06:33PM +0900, Changheun Lee wrote:
> > > > On Wed, Apr 07, 2021 at 09:16:12AM +0900, Changheun Lee wrote:
> > > > > > 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 <nanich.lee@samsung.com>
> > > > > > > > ---
> > > > > > > > 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?
> > > > >
> > > > > This patch is a solution for some inefficient case of multipage bvec like
> > > > > as current DIO scenario. So it's not set as a default.
> > > > > It will be set when bio size limitation is needed in runtime.
> > > >
> > > > Set where?
> > >
> > > In my environment, set it on init.rc file like as below.
> > > "echo 1 > /sys/block/sda/queue/limit_bio_size"
> >
> > I do not see any sysfs file in this patch, and why would you ever want
> > to be forced to manually do this? The hardware should know the limits
> > itself, and should automatically tune things like this, do not force a
> > user to do it as that's just not going to go well at all.
>
> Patch for sysfs is sent "[RESEND,v5,2/2] bio: add limit_bio_size sysfs".
> Actually I just suggested constant - 1MB - value to limit bio size at first.
> But I got a feedback that patch will be better if it's optional, and
> getting meaningful value from device queue on patchwork.
> There are some differences for each system environment I think.
>
> But there are inefficient logic obviously by applying of multipage bvec.
> So it will be shown in several system environment.
> Currently providing this patch as a option would be better to select
> according to each system environment, and policy I think.
>
> Please, revisit applying this patch.
>
> >
> > So if this patch series is forcing a new option to be configured by
> > sysfs only, that's not acceptable, sorry.
>
> If it is not acceptable ever with current, may I progress review again
> with default enabled?
I am sorry, I can not parse this, can you rephrase this?
thanks,
greg k-h
next prev parent reply other threads:[~2021-04-07 7:41 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20210316080104epcas1p11483035c927c2e65600ae90309334b24@epcas1p1.samsung.com>
2021-03-16 7:44 ` [RESEND PATCH v5 1/2] bio: limit bio max size Changheun Lee
[not found] ` <CGME20210316080106epcas1p3522dda95e9c97fc39b40b008bbf87c04@epcas1p3.samsung.com>
2021-03-16 7:44 ` [RESEND PATCH v5 2/2] bio: add limit_bio_size sysfs Changheun Lee
2021-04-06 21:05 ` Bart Van Assche
[not found] ` <CGME20210407013850epcas1p2d305f138c9fa1431abba1ec44a382de9@epcas1p2.samsung.com>
2021-04-07 1:21 ` Changheun Lee
2021-04-07 5:43 ` Greg KH
[not found] ` <CGME20210406014905epcas1p16830a46b7ac6af95a0e2c2c6f4c04859@epcas1p1.samsung.com>
2021-04-06 1:31 ` [RESEND PATCH v5 1/2] bio: limit bio max size Changheun Lee
2021-04-06 7:32 ` Greg KH
[not found] ` <CGME20210407003345epcas1p21376df37d3dfe933684139d3beaf9c51@epcas1p2.samsung.com>
2021-04-07 0:16 ` Changheun Lee
2021-04-07 5:05 ` Greg KH
[not found] ` <CGME20210407052407epcas1p1d0b5d23ac04a68760f691954e7ada3dd@epcas1p1.samsung.com>
2021-04-07 5:06 ` Changheun Lee
2021-04-07 5:36 ` Greg KH
[not found] ` <CGME20210407071241epcas1p2559ea674299b686c9001326894c933bc@epcas1p2.samsung.com>
2021-04-07 6:55 ` Changheun Lee
2021-04-07 7:40 ` Greg KH [this message]
[not found] ` <CGME20210407094610epcas1p472207e8d3ca0e5e697974c993a2a34f7@epcas1p4.samsung.com>
2021-04-07 9:28 ` [RESEND,v5,1/2] " Changheun Lee
2021-04-07 10:27 ` Damien Le Moal
2021-04-09 14:47 ` Bart Van Assche
2021-04-11 22:13 ` Damien Le Moal
2021-04-12 3:23 ` Ming Lei
[not found] ` <CGME20210413045517epcas1p32b058646dd795e59389401ca997c4cac@epcas1p3.samsung.com>
2021-04-13 4:37 ` Changheun Lee
2021-04-13 5:32 ` Christoph Hellwig
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