| Message ID | 20210720084320.184877-1-hch@lst.de (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [1/2] iomap: simplify iomap_readpage_actor | expand |
On Tue, Jul 20, 2021 at 10:43:19AM +0200, Christoph Hellwig wrote: > Now that the outstanding reads are counted in bytes, there is no need > to use the low-level __bio_try_merge_page API, we can switch back to > always using bio_add_page and simply iomap_readpage_actor again. I don't think this quite works. You need to check the return value from bio_add_page(), otherwise you can be in a situation where you try to add a page to the last bvec and it's not contiguous, so it fails. I was imagining something more like this: - bool same_page = false, is_contig = false; + bool is_contig = false; ... /* Try to merge into a previous segment if we can */ sector = iomap_sector(iomap, pos); - if (ctx->bio && bio_end_sector(ctx->bio) == sector) { - if (__bio_try_merge_page(ctx->bio, page, plen, poff, - &same_page)) - goto done; - is_contig = true; - } + if (ctx->bio && bio_end_sector(ctx->bio) == sector) + is_contig = bio_add_page(ctx->bio, page, plen, poff) > 0; - if (!is_contig || bio_full(ctx->bio, plen)) { + if (!is_contig) { gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL); gfp_t orig_gfp = gfp; ... bio_set_dev(ctx->bio, iomap->bdev); ctx->bio->bi_end_io = iomap_read_end_io; + bio_add_page(ctx->bio, page, plen, poff); } - bio_add_page(ctx->bio, page, plen, poff); done: /*
On Tue, Jul 20, 2021 at 01:27:24PM +0100, Matthew Wilcox wrote: > On Tue, Jul 20, 2021 at 10:43:19AM +0200, Christoph Hellwig wrote: > > Now that the outstanding reads are counted in bytes, there is no need > > to use the low-level __bio_try_merge_page API, we can switch back to > > always using bio_add_page and simply iomap_readpage_actor again. > > I don't think this quite works. You need to check the return value > from bio_add_page(), otherwise you can be in a situation where you try > to add a page to the last bvec and it's not contiguous, so it fails. Indeed. While bio_full covers the number of vectors, if we run out of bytes in bi_size this won't work. I think we can do this version, but I haven't tested it yet: --- From 4198cd5805d45f83c9029743ad5d0ce774a4e0f8 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig <hch@lst.de> Date: Mon, 12 Jul 2021 11:00:58 +0200 Subject: iomap: simplify iomap_readpage_actor Now that the outstanding reads are counted in bytes, there is no need to use the low-level __bio_try_merge_page API, we can switch back to always using bio_add_page and simply iomap_readpage_actor again. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/iomap/buffered-io.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 87ccb3438becd9..712b6513a0c449 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -241,7 +241,6 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct iomap_readpage_ctx *ctx = data; struct page *page = ctx->cur_page; struct iomap_page *iop; - bool same_page = false, is_contig = false; loff_t orig_pos = pos; unsigned poff, plen; sector_t sector; @@ -268,16 +267,10 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, if (iop) atomic_add(plen, &iop->read_bytes_pending); - /* Try to merge into a previous segment if we can */ sector = iomap_sector(iomap, pos); - if (ctx->bio && bio_end_sector(ctx->bio) == sector) { - if (__bio_try_merge_page(ctx->bio, page, plen, poff, - &same_page)) - goto done; - is_contig = true; - } - - if (!is_contig || bio_full(ctx->bio, plen)) { + if (!ctx->bio || + bio_end_sector(ctx->bio) != sector || + bio_add_page(ctx->bio, page, plen, poff) != plen) { gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL); gfp_t orig_gfp = gfp; unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE); @@ -301,9 +294,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, ctx->bio->bi_iter.bi_sector = sector; bio_set_dev(ctx->bio, iomap->bdev); ctx->bio->bi_end_io = iomap_read_end_io; + __bio_add_page(ctx->bio, page, plen, poff); } - - bio_add_page(ctx->bio, page, plen, poff); done: /* * Move the caller beyond our range so that it keeps making progress.
On Tue, Jul 20, 2021 at 03:26:44PM +0200, Christoph Hellwig wrote: > I think we can do this version, but I haven't tested it yet: I see no problems with this version. Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 87ccb3438becd9..4eaadbd265fcfa 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -241,7 +241,6 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct iomap_readpage_ctx *ctx = data; struct page *page = ctx->cur_page; struct iomap_page *iop; - bool same_page = false, is_contig = false; loff_t orig_pos = pos; unsigned poff, plen; sector_t sector; @@ -268,16 +267,10 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, if (iop) atomic_add(plen, &iop->read_bytes_pending); - /* Try to merge into a previous segment if we can */ sector = iomap_sector(iomap, pos); - if (ctx->bio && bio_end_sector(ctx->bio) == sector) { - if (__bio_try_merge_page(ctx->bio, page, plen, poff, - &same_page)) - goto done; - is_contig = true; - } - - if (!is_contig || bio_full(ctx->bio, plen)) { + if (!ctx->bio || + bio_full(ctx->bio, plen) || + bio_end_sector(ctx->bio) != sector) { gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL); gfp_t orig_gfp = gfp; unsigned int nr_vecs = DIV_ROUND_UP(length, PAGE_SIZE);
Now that the outstanding reads are counted in bytes, there is no need to use the low-level __bio_try_merge_page API, we can switch back to always using bio_add_page and simply iomap_readpage_actor again. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/iomap/buffered-io.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-)