Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: faXCfuO4aAyrsAYCq5MEyZDSAqop/qy5+ddUn2WytQbTFP6HbaoFPOU5TOQwonEH0H66lpXaRm
 1V7K+7xr5ULW4IRc22Y5j5JwtHCksrpJ6ZC1ntt/BhlHGoaaZyoT8RAhIHemX5igRW9sgnA68V
 HlpA5LCIYh4a/5IoyxMpuqVx7yLfXCOCOD3ttF+gMugTEITI9nRVCgaXGaALSqS2ecKOMUvZCt
 wAiY/cfW2DGxvZNm9adWa7m+F5FeymFz5qXUff91jedniJ+7ue1ygCXqlQmpHVLNndW7NNcCER
 6IU=
From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     Ming Lei <ming.lei@redhat.com>,
        Changheun Lee <nanich.lee@samsung.com>
CC:     Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
        "asml.silence@gmail.com" <asml.silence@gmail.com>,
        "axboe@kernel.dk" <axboe@kernel.dk>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "osandov@fb.com" <osandov@fb.com>,
        "patchwork-bot@kernel.org" <patchwork-bot@kernel.org>,
        "tj@kernel.org" <tj@kernel.org>,
        "tom.leiming@gmail.com" <tom.leiming@gmail.com>,
        "jisoo2146.oh@samsung.com" <jisoo2146.oh@samsung.com>,
        "junho89.kim@samsung.com" <junho89.kim@samsung.com>,
        "mj0123.lee@samsung.com" <mj0123.lee@samsung.com>,
        "seunghwan.hyun@samsung.com" <seunghwan.hyun@samsung.com>,
        "sookwan7.kim@samsung.com" <sookwan7.kim@samsung.com>,
        "woosung2.lee@samsung.com" <woosung2.lee@samsung.com>,
        "yt0928.kim@samsung.com" <yt0928.kim@samsung.com>
Subject: Re: [PATCH v3 1/2] bio: limit bio max size
Thread-Topic: [PATCH v3 1/2] bio: limit bio max size
Thread-Index: AQHW84VRloabNXvGbkml+gtfdHfb2g==
Date:   Tue, 26 Jan 2021 04:06:06 +0000
Message-ID: <BL0PR04MB65143B60B6062996764423C3E7BC9@BL0PR04MB6514.namprd04.prod.outlook.com>
References: <CGME20210126014805epcas1p2c4fc40f01c9c89b0a94ff6cac5408347@epcas1p2.samsung.com>
 <20210126013235.28711-1-nanich.lee@samsung.com>
 <20210126035748.GA1071341@T590>
Accept-Language: en-US
Content-Language: en-US
wdcipoutbound: EOP-TRUE
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: a4080feb-7e04-47a9-ab94-08d8c1afb4b3
X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Jan 2021 04:06:06.6562
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: siaVA2kWAOz3g/JpkmKlmGTuBF6h6bcVnplaMEd3xgYPpo8Dh24Q315Gjmdr5Gl47T2VtVW59lRSz01gY9wMfg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL0PR04MB4610
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 2021/01/26 12:58, Ming Lei wrote:=0A=
> On Tue, Jan 26, 2021 at 10:32:34AM +0900, Changheun Lee wrote:=0A=
>> bio size can grow up to 4GB when muli-page bvec is enabled.=0A=
>> but sometimes it would lead to inefficient behaviors.=0A=
>> in case of large chunk direct I/O, - 32MB chunk read in user space -=0A=
>> all pages for 32MB would be merged to a bio structure if the pages=0A=
>> physical addresses are contiguous. it makes some delay to submit=0A=
>> until merge complete. bio max size should be limited to a proper size.=
=0A=
>>=0A=
>> When 32MB chunk read with direct I/O option is coming from userspace,=0A=
>> kernel behavior is below now. it's timeline.=0A=
>>=0A=
>>  | bio merge for 32MB. total 8,192 pages are merged.=0A=
>>  | total elapsed time is over 2ms.=0A=
>>  |------------------ ... ----------------------->|=0A=
>>                                                  | 8,192 pages merged a =
bio.=0A=
>>                                                  | at this time, first b=
io submit is done.=0A=
>>                                                  | 1 bio is split to 32 =
read request and issue.=0A=
>>                                                  |--------------->=0A=
>>                                                   |--------------->=0A=
>>                                                    |--------------->=0A=
>>                                                               ......=0A=
>>                                                                    |----=
----------->=0A=
>>                                                                     |---=
------------>|=0A=
>>                           total 19ms elapsed to complete 32MB read done =
from device. |=0A=
>>=0A=
>> If bio max size is limited with 1MB, behavior is changed below.=0A=
>>=0A=
>>  | bio merge for 1MB. 256 pages are merged for each bio.=0A=
>>  | total 32 bio will be made.=0A=
>>  | total elapsed time is over 2ms. it's same.=0A=
>>  | but, first bio submit timing is fast. about 100us.=0A=
>>  |--->|--->|--->|---> ... -->|--->|--->|--->|--->|=0A=
>>       | 256 pages merged a bio.=0A=
>>       | at this time, first bio submit is done.=0A=
>>       | and 1 read request is issued for 1 bio.=0A=
>>       |--------------->=0A=
>>            |--------------->=0A=
>>                 |--------------->=0A=
>>                                       ......=0A=
>>                                                  |--------------->=0A=
>>                                                   |--------------->|=0A=
>>         total 17ms elapsed to complete 32MB read done from device. |=0A=
>>=0A=
>> As a result, read request issue timing is faster if bio max size is limi=
ted.=0A=
>> Current kernel behavior with multipage bvec, super large bio can be crea=
ted.=0A=
>> And it lead to delay first I/O request issue.=0A=
>>=0A=
>> Signed-off-by: Changheun Lee <nanich.lee@samsung.com>=0A=
>> ---=0A=
>>  block/bio.c            | 17 ++++++++++++++++-=0A=
>>  include/linux/bio.h    |  4 +++-=0A=
>>  include/linux/blkdev.h |  3 +++=0A=
>>  3 files changed, 22 insertions(+), 2 deletions(-)=0A=
>>=0A=
>> diff --git a/block/bio.c b/block/bio.c=0A=
>> index 1f2cc1fbe283..ec0281889045 100644=0A=
>> --- a/block/bio.c=0A=
>> +++ b/block/bio.c=0A=
>> @@ -287,6 +287,21 @@ void bio_init(struct bio *bio, struct bio_vec *tabl=
e,=0A=
>>  }=0A=
>>  EXPORT_SYMBOL(bio_init);=0A=
>>  =0A=
>> +unsigned int bio_max_size(struct bio *bio)=0A=
>> +{=0A=
>> +	struct request_queue *q;=0A=
>> +=0A=
>> +	if (!bio->bi_disk)=0A=
>> +		return UINT_MAX;=0A=
>> +=0A=
>> +	q =3D bio->bi_disk->queue;=0A=
>> +	if (!blk_queue_limit_bio_size(q))=0A=
>> +		return UINT_MAX;=0A=
>> +=0A=
>> +	return blk_queue_get_max_sectors(q, bio_op(bio)) << SECTOR_SHIFT;=0A=
>> +}=0A=
>> +EXPORT_SYMBOL(bio_max_size);=0A=
>> +=0A=
>>  /**=0A=
>>   * bio_reset - reinitialize a bio=0A=
>>   * @bio:	bio to reset=0A=
>> @@ -877,7 +892,7 @@ bool __bio_try_merge_page(struct bio *bio, struct pa=
ge *page,=0A=
>>  		struct bio_vec *bv =3D &bio->bi_io_vec[bio->bi_vcnt - 1];=0A=
>>  =0A=
>>  		if (page_is_mergeable(bv, page, len, off, same_page)) {=0A=
>> -			if (bio->bi_iter.bi_size > UINT_MAX - len) {=0A=
>> +			if (bio->bi_iter.bi_size > bio_max_size(bio) - len) {=0A=
>>  				*same_page =3D false;=0A=
>>  				return false;=0A=
>>  			}=0A=
> =0A=
> So far we don't need bio->bi_disk or bio->bi_bdev(will be changed in=0A=
> Christoph's patch) during adding page to bio, so there is null ptr=0A=
> refereance risk.=0A=
> =0A=
>> diff --git a/include/linux/bio.h b/include/linux/bio.h=0A=
>> index 1edda614f7ce..cdb134ca7bf5 100644=0A=
>> --- a/include/linux/bio.h=0A=
>> +++ b/include/linux/bio.h=0A=
>> @@ -100,6 +100,8 @@ static inline void *bio_data(struct bio *bio)=0A=
>>  	return NULL;=0A=
>>  }=0A=
>>  =0A=
>> +extern unsigned int bio_max_size(struct bio *);=0A=
>> +=0A=
>>  /**=0A=
>>   * bio_full - check if the bio is full=0A=
>>   * @bio:	bio to check=0A=
>> @@ -113,7 +115,7 @@ static inline bool bio_full(struct bio *bio, unsigne=
d len)=0A=
>>  	if (bio->bi_vcnt >=3D bio->bi_max_vecs)=0A=
>>  		return true;=0A=
>>  =0A=
>> -	if (bio->bi_iter.bi_size > UINT_MAX - len)=0A=
>> +	if (bio->bi_iter.bi_size > bio_max_size(bio) - len)=0A=
>>  		return true;=0A=
>>  =0A=
>>  	return false;=0A=
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h=0A=
>> index f94ee3089e01..3aeab9e7e97b 100644=0A=
>> --- a/include/linux/blkdev.h=0A=
>> +++ b/include/linux/blkdev.h=0A=
>> @@ -621,6 +621,7 @@ struct request_queue {=0A=
>>  #define QUEUE_FLAG_RQ_ALLOC_TIME 27	/* record rq->alloc_time_ns */=0A=
>>  #define QUEUE_FLAG_HCTX_ACTIVE	28	/* at least one blk-mq hctx is active=
 */=0A=
>>  #define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */=0A=
>> +#define QUEUE_FLAG_LIMIT_BIO_SIZE 30	/* limit bio size */=0A=
>>  =0A=
>>  #define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\=0A=
>>  				 (1 << QUEUE_FLAG_SAME_COMP) |		\=0A=
>> @@ -667,6 +668,8 @@ bool blk_queue_flag_test_and_set(unsigned int flag, =
struct request_queue *q);=0A=
>>  #define blk_queue_fua(q)	test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags)=0A=
>>  #define blk_queue_registered(q)	test_bit(QUEUE_FLAG_REGISTERED, &(q)->q=
ueue_flags)=0A=
>>  #define blk_queue_nowait(q)	test_bit(QUEUE_FLAG_NOWAIT, &(q)->queue_fla=
gs)=0A=
>> +#define blk_queue_limit_bio_size(q)	\=0A=
>> +	test_bit(QUEUE_FLAG_LIMIT_BIO_SIZE, &(q)->queue_flags)=0A=
> =0A=
> I don't think it is a good idea by adding queue flag for this purpose,=0A=
> since this case just needs to limit bio size for not delay bio submission=
=0A=
> too much, which is kind of logical thing, nothing to do with request queu=
e.=0A=
> =0A=
> Just wondering why you don't take the following way:=0A=
> =0A=
> =0A=
> diff --git a/block/bio.c b/block/bio.c=0A=
> index 99040a7e6656..35852f7f47d4 100644=0A=
> --- a/block/bio.c=0A=
> +++ b/block/bio.c=0A=
> @@ -1081,7 +1081,7 @@ static int __bio_iov_append_get_pages(struct bio *b=
io, struct iov_iter *iter)=0A=
>   * It's intended for direct IO, so doesn't do PSI tracking, the caller i=
s=0A=
>   * responsible for setting BIO_WORKINGSET if necessary.=0A=
>   */=0A=
> -int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)=0A=
> +int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter, bool =
sync)=0A=
>  {=0A=
>  	int ret =3D 0;=0A=
>  =0A=
> @@ -1092,12 +1092,20 @@ int bio_iov_iter_get_pages(struct bio *bio, struc=
t iov_iter *iter)=0A=
>  		bio_set_flag(bio, BIO_NO_PAGE_REF);=0A=
>  		return 0;=0A=
>  	} else {=0A=
> +		/*=0A=
> +		 * Don't add too many pages in case of sync dio for=0A=
> +		 * avoiding delay bio submission too much especially=0A=
> +		 * pinning user pages in memory isn't cheap.=0A=
> +		 */=0A=
> +		const unsigned int max_size =3D sync ? (1U << 12) : UINT_MAX;=0A=
=0A=
4KB max bio size ? That is a little small :)=0A=
In any case, I am not a fan of using an arbitrary value not related to the=
=0A=
actual device characteristics. Wouldn't it be better to us the device=0A=
max_sectors limit ? And that limit would need to be zone_append_max_sectors=
 for=0A=
zone append writes. So some helper like Changheun bio_max_size() may be use=
ful.=0A=
=0A=
Apart from this point, I like your approach.=0A=
=0A=
> +=0A=
>  		do {=0A=
>  			if (bio_op(bio) =3D=3D REQ_OP_ZONE_APPEND)=0A=
>  				ret =3D __bio_iov_append_get_pages(bio, iter);=0A=
>  			else=0A=
>  				ret =3D __bio_iov_iter_get_pages(bio, iter);=0A=
> -		} while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));=0A=
> +		} while (!ret && iov_iter_count(iter) && !bio_full(bio, 0) &&=0A=
> +				bio->bi_iter.bi_size < max_size);=0A=
>  	}=0A=
>  =0A=
>  	/* don't account direct I/O as memory stall */=0A=
> diff --git a/fs/block_dev.c b/fs/block_dev.c=0A=
> index 6f5bd9950baf..0d1d436aca17 100644=0A=
> --- a/fs/block_dev.c=0A=
> +++ b/fs/block_dev.c=0A=
> @@ -246,7 +246,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct =
iov_iter *iter,=0A=
>  	bio.bi_end_io =3D blkdev_bio_end_io_simple;=0A=
>  	bio.bi_ioprio =3D iocb->ki_ioprio;=0A=
>  =0A=
> -	ret =3D bio_iov_iter_get_pages(&bio, iter);=0A=
> +	ret =3D bio_iov_iter_get_pages(&bio, iter, true);=0A=
>  	if (unlikely(ret))=0A=
>  		goto out;=0A=
>  	ret =3D bio.bi_iter.bi_size;=0A=
> @@ -397,7 +397,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_ite=
r *iter, int nr_pages)=0A=
>  		bio->bi_end_io =3D blkdev_bio_end_io;=0A=
>  		bio->bi_ioprio =3D iocb->ki_ioprio;=0A=
>  =0A=
> -		ret =3D bio_iov_iter_get_pages(bio, iter);=0A=
> +		ret =3D bio_iov_iter_get_pages(bio, iter, is_sync);=0A=
>  		if (unlikely(ret)) {=0A=
>  			bio->bi_status =3D BLK_STS_IOERR;=0A=
>  			bio_endio(bio);=0A=
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c=0A=
> index ea1e8f696076..5105982a9bf8 100644=0A=
> --- a/fs/iomap/direct-io.c=0A=
> +++ b/fs/iomap/direct-io.c=0A=
> @@ -277,7 +277,8 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, =
loff_t length,=0A=
>  		bio->bi_private =3D dio;=0A=
>  		bio->bi_end_io =3D iomap_dio_bio_end_io;=0A=
>  =0A=
> -		ret =3D bio_iov_iter_get_pages(bio, dio->submit.iter);=0A=
> +		ret =3D bio_iov_iter_get_pages(bio, dio->submit.iter,=0A=
> +				is_sync_kiocb(dio->iocb));=0A=
>  		if (unlikely(ret)) {=0A=
>  			/*=0A=
>  			 * We have to stop part way through an IO. We must fall=0A=
> diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c=0A=
> index bec47f2d074b..c95ac37f9305 100644=0A=
> --- a/fs/zonefs/super.c=0A=
> +++ b/fs/zonefs/super.c=0A=
> @@ -690,7 +690,7 @@ static ssize_t zonefs_file_dio_append(struct kiocb *i=
ocb, struct iov_iter *from)=0A=
>  	if (iocb->ki_flags & IOCB_DSYNC)=0A=
>  		bio->bi_opf |=3D REQ_FUA;=0A=
>  =0A=
> -	ret =3D bio_iov_iter_get_pages(bio, from);=0A=
> +	ret =3D bio_iov_iter_get_pages(bio, from, is_sync_kiocb(iocb));=0A=
>  	if (unlikely(ret))=0A=
>  		goto out_release;=0A=
>  =0A=
> diff --git a/include/linux/bio.h b/include/linux/bio.h=0A=
> index 676870b2c88d..fa3a503b955c 100644=0A=
> --- a/include/linux/bio.h=0A=
> +++ b/include/linux/bio.h=0A=
> @@ -472,7 +472,7 @@ bool __bio_try_merge_page(struct bio *bio, struct pag=
e *page,=0A=
>  		unsigned int len, unsigned int off, bool *same_page);=0A=
>  void __bio_add_page(struct bio *bio, struct page *page,=0A=
>  		unsigned int len, unsigned int off);=0A=
> -int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);=0A=
> +int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter, bool =
sync);=0A=
>  void bio_release_pages(struct bio *bio, bool mark_dirty);=0A=
>  extern void bio_set_pages_dirty(struct bio *bio);=0A=
>  extern void bio_check_pages_dirty(struct bio *bio);=0A=
> =0A=
> =0A=
> Thanks,=0A=
> Ming=0A=
> =0A=
> =0A=
=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=