On Tue, Mar 31, 2020 at 08:04:21PM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>
> bio_alloc() can fail when we use GFP_NORETRY. If it does, allocate
> a bio large enough for a single page like mpage_readpages() does.
Why does mpage_readpages() do that?
Is this a means to guarantee some kind of forward (readahead?) progress?
Forgive my ignorance, but if memory is so tight we can't allocate a bio
for readahead then why not exit having accomplished nothing?
--D
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> fs/iomap/buffered-io.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 417115bfaf6b..c258801f18d4 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -302,6 +302,7 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>
> if (!ctx->bio || !is_contig || bio_full(ctx->bio, plen)) {
> gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
> + gfp_t orig_gfp = gfp;
> int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
>
> if (ctx->bio)
> @@ -310,6 +311,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> if (ctx->is_readahead) /* same as readahead_gfp_mask */
> gfp |= __GFP_NORETRY | __GFP_NOWARN;
> ctx->bio = bio_alloc(gfp, min(BIO_MAX_PAGES, nr_vecs));
> + if (!ctx->bio)
> + ctx->bio = bio_alloc(orig_gfp, 1);
> ctx->bio->bi_opf = REQ_OP_READ;
> if (ctx->is_readahead)
> ctx->bio->bi_opf |= REQ_RAHEAD;
> --
> 2.25.1
>
