| Message ID | 20210604050324.28670-2-nanich.lee@samsung.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v12,1/3] bio: control bio max size | expand |
On 2021/06/04 14:22, Changheun Lee wrote: > bio size can grow up to 4GB after muli-page bvec has been enabled. > But sometimes large size of bio would lead to inefficient behaviors. > Control of bio max size will be helpful to improve inefficiency. > > Below is a example for inefficient behaviours. > 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 | 17 ++++++++++++++--- > block/blk-settings.c | 19 +++++++++++++++++++ > include/linux/bio.h | 4 +++- > include/linux/blkdev.h | 3 +++ > 4 files changed, 39 insertions(+), 4 deletions(-) > > diff --git a/block/bio.c b/block/bio.c > index 44205dfb6b60..73b673f1684e 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -255,6 +255,13 @@ void bio_init(struct bio *bio, struct bio_vec *table, > } > EXPORT_SYMBOL(bio_init); > > +unsigned int bio_max_bytes(struct bio *bio) > +{ > + struct block_device *bdev = bio->bi_bdev; > + > + return bdev ? bdev->bd_disk->queue->limits.max_bio_bytes : UINT_MAX; > +} unsigned int bio_max_bytes(struct bio *bio) { struct block_device *bdev = bio->bi_bdev; if (!bdev) return UINT_MAX; return bdev->bd_disk->queue->limits.max_bio_bytes; } is a lot more readable... Also, I remember there was some problems with bd_disk possibly being null. Was that fixed ? > + > /** > * bio_reset - reinitialize a bio > * @bio: bio to reset > @@ -866,7 +873,7 @@ 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_bytes(bio) - len) { > *same_page = false; > return false; > } > @@ -995,6 +1002,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) > { > unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt; > unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; > + unsigned int bytes_left = bio_max_bytes(bio) - bio->bi_iter.bi_size; > struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; > struct page **pages = (struct page **)bv; > bool same_page = false; > @@ -1010,7 +1018,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) > BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2); > pages += entries_left * (PAGE_PTRS_PER_BVEC - 1); > > - size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); > + size = iov_iter_get_pages(iter, pages, bytes_left, nr_pages, > + &offset); > if (unlikely(size <= 0)) > return size ? size : -EFAULT; > > @@ -1038,6 +1047,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) > { > unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt; > unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; > + unsigned int bytes_left = bio_max_bytes(bio) - bio->bi_iter.bi_size; > struct request_queue *q = bio->bi_bdev->bd_disk->queue; > unsigned int max_append_sectors = queue_max_zone_append_sectors(q); > struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; > @@ -1058,7 +1068,8 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) > BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2); > pages += entries_left * (PAGE_PTRS_PER_BVEC - 1); > > - size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); > + size = iov_iter_get_pages(iter, pages, bytes_left, nr_pages, > + &offset); > if (unlikely(size <= 0)) > return size ? size : -EFAULT; > > diff --git a/block/blk-settings.c b/block/blk-settings.c > index 902c40d67120..e270e31519a1 100644 > --- a/block/blk-settings.c > +++ b/block/blk-settings.c > @@ -32,6 +32,7 @@ EXPORT_SYMBOL_GPL(blk_queue_rq_timeout); > */ > void blk_set_default_limits(struct queue_limits *lim) > { > + lim->max_bio_bytes = UINT_MAX; > lim->max_segments = BLK_MAX_SEGMENTS; > lim->max_discard_segments = 1; > lim->max_integrity_segments = 0; > @@ -100,6 +101,24 @@ void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce bounce) > } > EXPORT_SYMBOL(blk_queue_bounce_limit); > > +/** > + * blk_queue_max_bio_bytes - set bio max size for queue blk_queue_max_bio_bytes - set max_bio_bytes queue limit And then you can drop the not very useful description. > + * @q: the request queue for the device > + * @bytes : bio max bytes to be set > + * > + * Description: > + * Set proper bio max size to optimize queue operating. > + **/ > +void blk_queue_max_bio_bytes(struct request_queue *q, unsigned int bytes) > +{ > + struct queue_limits *limits = &q->limits; > + unsigned int max_bio_bytes = round_up(bytes, PAGE_SIZE); > + > + limits->max_bio_bytes = max_t(unsigned int, max_bio_bytes, > + BIO_MAX_VECS * PAGE_SIZE); > +} > +EXPORT_SYMBOL(blk_queue_max_bio_bytes); Setting of the stacked limits is still missing. > + > /** > * blk_queue_max_hw_sectors - set max sectors for a request for this queue > * @q: the request queue for the device > diff --git a/include/linux/bio.h b/include/linux/bio.h > index a0b4cfdf62a4..3959cc1a0652 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -106,6 +106,8 @@ static inline void *bio_data(struct bio *bio) > return NULL; > } > > +extern unsigned int bio_max_bytes(struct bio *bio); > + > /** > * bio_full - check if the bio is full > * @bio: bio to check > @@ -119,7 +121,7 @@ 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_bytes(bio) - len) > return true; > > return false; > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h > index 1255823b2bc0..861888501fc0 100644 > --- a/include/linux/blkdev.h > +++ b/include/linux/blkdev.h > @@ -326,6 +326,8 @@ enum blk_bounce { > }; > > struct queue_limits { > + unsigned int max_bio_bytes; > + > enum blk_bounce bounce; > unsigned long seg_boundary_mask; > unsigned long virt_boundary_mask; > @@ -1132,6 +1134,7 @@ extern void blk_abort_request(struct request *); > * Access functions for manipulating queue properties > */ > extern void blk_cleanup_queue(struct request_queue *); > +extern void blk_queue_max_bio_bytes(struct request_queue *, unsigned int); > void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce limit); > extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int); > extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int); >
NAK. As discussed countless time we already have an actual limit. And we can look it as advisory before building ever bigger bios, but the last thing we need is yet another confusing limit.
On Fri, Jun 04, 2021 at 07:52:35AM -0700, Bart Van Assche wrote:
> Damien is right. bd_disk can be NULL. From
bd_disk is initialized in bdev_alloc, so it should never be NULL.
bi_bdev OTOH is only set afer bio_add_page in various places or not at
all in case of passthrough bios. Which is a bit of a mess and I have
plans to fix it.
> NAK. As discussed countless time we already have an actual limit. > And we can look it as advisory before building ever bigger bios, > but the last thing we need is yet another confusing limit. Thank you for your review and feedback. I has thought proper bio size control with proper interface might be good, and can be helpful to the other module beside issued performance problem. Providing of common interface to control bio size in block layer might be good I think even though current patch is not accepted. Thanks for all, Changheun Lee
On 6/6/21 11:35 PM, Christoph Hellwig wrote: > On Fri, Jun 04, 2021 at 07:52:35AM -0700, Bart Van Assche wrote: >> Damien is right. bd_disk can be NULL. From > > bd_disk is initialized in bdev_alloc, so it should never be NULL. > bi_bdev OTOH is only set afer bio_add_page in various places or not at > all in case of passthrough bios. Which is a bit of a mess and I have > plans to fix it. Hi Christoph, Thank you for having shared your plans for how to improve how bi_bdev is set. In case you would not yet have had the time to do this, please take a look at the call trace available on https://lore.kernel.org/linux-block/20210425043020.30065-1-bvanassche@acm.org/. That call trace shows how bio_add_pc_page() is called by the SCSI core before alloc_disk() is called. I think that sending a SCSI command before alloc_disk() is called is fundamental in the SCSI core because the SCSI INQUIRY command has to be sent before it is known whether or not a SCSI LUN represents a disk. Thanks, Bart.
On Mon, Jun 07, 2021 at 09:46:56AM -0700, Bart Van Assche wrote: > In case you would not yet have had the time to do this, please take a > look at the call trace available on > https://lore.kernel.org/linux-block/20210425043020.30065-1-bvanassche@acm.org/. > That call trace shows how bio_add_pc_page() is called by the SCSI core > before alloc_disk() is called. I think that sending a SCSI command > before alloc_disk() is called is fundamental in the SCSI core because > the SCSI INQUIRY command has to be sent before it is known whether or > not a SCSI LUN represents a disk. I have a plan for that as well, stay tuned :)
diff --git a/block/bio.c b/block/bio.c index 44205dfb6b60..73b673f1684e 100644 --- a/block/bio.c +++ b/block/bio.c @@ -255,6 +255,13 @@ void bio_init(struct bio *bio, struct bio_vec *table, } EXPORT_SYMBOL(bio_init); +unsigned int bio_max_bytes(struct bio *bio) +{ + struct block_device *bdev = bio->bi_bdev; + + return bdev ? bdev->bd_disk->queue->limits.max_bio_bytes : UINT_MAX; +} + /** * bio_reset - reinitialize a bio * @bio: bio to reset @@ -866,7 +873,7 @@ 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_bytes(bio) - len) { *same_page = false; return false; } @@ -995,6 +1002,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) { unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt; unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; + unsigned int bytes_left = bio_max_bytes(bio) - bio->bi_iter.bi_size; struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; struct page **pages = (struct page **)bv; bool same_page = false; @@ -1010,7 +1018,8 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter) BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2); pages += entries_left * (PAGE_PTRS_PER_BVEC - 1); - size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); + size = iov_iter_get_pages(iter, pages, bytes_left, nr_pages, + &offset); if (unlikely(size <= 0)) return size ? size : -EFAULT; @@ -1038,6 +1047,7 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) { unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt; unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt; + unsigned int bytes_left = bio_max_bytes(bio) - bio->bi_iter.bi_size; struct request_queue *q = bio->bi_bdev->bd_disk->queue; unsigned int max_append_sectors = queue_max_zone_append_sectors(q); struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt; @@ -1058,7 +1068,8 @@ static int __bio_iov_append_get_pages(struct bio *bio, struct iov_iter *iter) BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2); pages += entries_left * (PAGE_PTRS_PER_BVEC - 1); - size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); + size = iov_iter_get_pages(iter, pages, bytes_left, nr_pages, + &offset); if (unlikely(size <= 0)) return size ? size : -EFAULT; diff --git a/block/blk-settings.c b/block/blk-settings.c index 902c40d67120..e270e31519a1 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -32,6 +32,7 @@ EXPORT_SYMBOL_GPL(blk_queue_rq_timeout); */ void blk_set_default_limits(struct queue_limits *lim) { + lim->max_bio_bytes = UINT_MAX; lim->max_segments = BLK_MAX_SEGMENTS; lim->max_discard_segments = 1; lim->max_integrity_segments = 0; @@ -100,6 +101,24 @@ void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce bounce) } EXPORT_SYMBOL(blk_queue_bounce_limit); +/** + * blk_queue_max_bio_bytes - set bio max size for queue + * @q: the request queue for the device + * @bytes : bio max bytes to be set + * + * Description: + * Set proper bio max size to optimize queue operating. + **/ +void blk_queue_max_bio_bytes(struct request_queue *q, unsigned int bytes) +{ + struct queue_limits *limits = &q->limits; + unsigned int max_bio_bytes = round_up(bytes, PAGE_SIZE); + + limits->max_bio_bytes = max_t(unsigned int, max_bio_bytes, + BIO_MAX_VECS * PAGE_SIZE); +} +EXPORT_SYMBOL(blk_queue_max_bio_bytes); + /** * blk_queue_max_hw_sectors - set max sectors for a request for this queue * @q: the request queue for the device diff --git a/include/linux/bio.h b/include/linux/bio.h index a0b4cfdf62a4..3959cc1a0652 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -106,6 +106,8 @@ static inline void *bio_data(struct bio *bio) return NULL; } +extern unsigned int bio_max_bytes(struct bio *bio); + /** * bio_full - check if the bio is full * @bio: bio to check @@ -119,7 +121,7 @@ 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_bytes(bio) - len) return true; return false; diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 1255823b2bc0..861888501fc0 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -326,6 +326,8 @@ enum blk_bounce { }; struct queue_limits { + unsigned int max_bio_bytes; + enum blk_bounce bounce; unsigned long seg_boundary_mask; unsigned long virt_boundary_mask; @@ -1132,6 +1134,7 @@ extern void blk_abort_request(struct request *); * Access functions for manipulating queue properties */ extern void blk_cleanup_queue(struct request_queue *); +extern void blk_queue_max_bio_bytes(struct request_queue *, unsigned int); void blk_queue_bounce_limit(struct request_queue *q, enum blk_bounce limit); extern void blk_queue_max_hw_sectors(struct request_queue *, unsigned int); extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
bio size can grow up to 4GB after muli-page bvec has been enabled. But sometimes large size of bio would lead to inefficient behaviors. Control of bio max size will be helpful to improve inefficiency. Below is a example for inefficient behaviours. 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 | 17 ++++++++++++++--- block/blk-settings.c | 19 +++++++++++++++++++ include/linux/bio.h | 4 +++- include/linux/blkdev.h | 3 +++ 4 files changed, 39 insertions(+), 4 deletions(-)