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Date: Tue, 12 Jan 2021 09:16:56 +0000 From: Damien Le Moal <Damien.LeMoal@....com> To: Changheun Lee <nanich.lee@...sung.com>, "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "axboe@...nel.dk" <axboe@...nel.dk>, Johannes Thumshirn <Johannes.Thumshirn@....com>, "tj@...nel.org" <tj@...nel.org> CC: "seunghwan.hyun@...sung.com" <seunghwan.hyun@...sung.com>, "sookwan7.kim@...sung.com" <sookwan7.kim@...sung.com>, "yt0928.kim@...sung.com" <yt0928.kim@...sung.com>, "mj0123.lee@...sung.com" <mj0123.lee@...sung.com>, "junho89.kim@...sung.com" <junho89.kim@...sung.com>, "jisoo2146.oh@...sung.com" <jisoo2146.oh@...sung.com> Subject: Re: [PATCH] bio: limit bio max size. On 2021/01/12 17:52, Changheun Lee wrote: > From: "Changheun Lee" <nanich.lee@...sung.com> > > 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, - 64MB chunk read in user space - > all pages for 64MB would be merged to a bio structure if memory address is > continued phsycally. it makes some delay to submit until merge complete. > bio max size should be limited as a proper size. But merging physically contiguous pages into the same bvec + later automatic bio split on submit should give you better throughput for large IOs compared to having to issue a bio chain of smaller BIOs that are arbitrarily sized and will likely need splitting anyway (because of DMA boundaries etc). Do you have a specific case where you see higher performance with this patch applied ? On Intel, BIO_MAX_SIZE would be 1MB... That is arbitrary and too small considering that many hardware can execute larger IOs than that. > > Signed-off-by: Changheun Lee <nanich.lee@...sung.com> > --- > block/bio.c | 2 +- > include/linux/bio.h | 3 ++- > 2 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/block/bio.c b/block/bio.c > index 1f2cc1fbe283..dbe14d675f28 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -877,7 +877,7 @@ 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 - len) { > *same_page = false; > return false; > } > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 1edda614f7ce..0f49b354b1f6 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -20,6 +20,7 @@ > #endif > > #define BIO_MAX_PAGES 256 > +#define BIO_MAX_SIZE (BIO_MAX_PAGES * PAGE_SIZE) > > #define bio_prio(bio) (bio)->bi_ioprio > #define bio_set_prio(bio, prio) ((bio)->bi_ioprio = prio) > @@ -113,7 +114,7 @@ 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 - len) > return true; > > return false; > -- Damien Le Moal Western Digital Research
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