Hi Matthew, On Tue, Aug 08, 2017 at 05:49:59AM -0700, Matthew Wilcox wrote: > On Tue, Aug 08, 2017 at 03:50:20PM +0900, Minchan Kim wrote: > > There is no need to use dynamic bio allocation for BDI_CAP_SYNC > > devices. They can with on-stack-bio without concern about waiting > > bio allocation from mempool under heavy memory pressure. > > This seems ... more complex than necessary? Why not simply do this: > > diff --git a/fs/mpage.c b/fs/mpage.c > index baff8f820c29..6db6bf5131ed 100644 > --- a/fs/mpage.c > +++ b/fs/mpage.c > @@ -157,6 +157,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages, > unsigned page_block; > unsigned first_hole = blocks_per_page; > struct block_device *bdev = NULL; > + struct bio sbio; > + struct bio_vec sbvec; > int length; > int fully_mapped = 1; > unsigned nblocks; > @@ -281,10 +283,17 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages, > page)) > goto out; > } > - bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), > + if (bdi_cap_synchronous_io(inode_to_bdi(inode))) { > + bio = &sbio; > + bio_init(bio, &sbvec, nr_pages); > + sbio.bi_bdev = bdev; > + sbio.bi_iter.bi_sector = blocks[0] << (blkbits - 9); > + } else { > + bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9), > min_t(int, nr_pages, BIO_MAX_PAGES), gfp); > - if (bio == NULL) > - goto confused; > + if (bio == NULL) > + goto confused; > + } > } > > length = first_hole << blkbits; > @@ -301,6 +310,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages, > else > *last_block_in_bio = blocks[blocks_per_page - 1]; > out: > + if (bio == &sbio) > + bio = mpage_bio_submit(REQ_OP_READ, 0, bio); Looks nicer but one nitpick: For reusing mpage_bio_submit, we need to call bio_get for on-stack-bio which doesn't make sense to me but if you think it's more readable and ok with overhead with two unnecessary atomic instructions(bio_get/put), I will do it in next spin. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>