| Message ID | 20210715033704.692967-91-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Memory folios | expand |
On Thu, Jul 15, 2021 at 04:36:16AM +0100, Matthew Wilcox (Oracle) wrote: > This is a thin wrapper around bio_add_page(). The main advantage here > is the documentation that the submitter can expect to see folios in the > completion handler, and that stupidly large folios are not supported. > It's not currently possible to allocate stupidly large folios, but if > it ever becomes possible, this function will fail gracefully instead of > doing I/O to the wrong bytes. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > block/bio.c | 21 +++++++++++++++++++++ > include/linux/bio.h | 3 ++- > 2 files changed, 23 insertions(+), 1 deletion(-) > > diff --git a/block/bio.c b/block/bio.c > index 1fab762e079b..1b500611d25c 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -933,6 +933,27 @@ int bio_add_page(struct bio *bio, struct page *page, > } > EXPORT_SYMBOL(bio_add_page); > > +/** > + * bio_add_folio - Attempt to add part of a folio to a bio. > + * @bio: Bio to add to. > + * @folio: Folio to add. > + * @len: How many bytes from the folio to add. > + * @off: First byte in this folio to add. > + * > + * Always uses the head page of the folio in the bio. If a submitter > + * only uses bio_add_folio(), it can count on never seeing tail pages > + * in the completion routine. BIOs do not support folios larger than 2GiB. > + * > + * Return: The number of bytes from this folio added to the bio. > + */ > +size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len, > + size_t off) > +{ > + if (len > UINT_MAX || off > UINT_MAX) Er... if bios don't support folios larger than 2GB, then why check @off and @len against UINT_MAX, which is ~4GB? --D > + return 0; > + return bio_add_page(bio, &folio->page, len, off); > +} > + > void bio_release_pages(struct bio *bio, bool mark_dirty) > { > struct bvec_iter_all iter_all; > diff --git a/include/linux/bio.h b/include/linux/bio.h > index 2203b686e1f0..ade93e2de6a1 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -462,7 +462,8 @@ extern void bio_uninit(struct bio *); > extern void bio_reset(struct bio *); > void bio_chain(struct bio *, struct bio *); > > -extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int); > +int bio_add_page(struct bio *, struct page *, unsigned len, unsigned off); > +size_t bio_add_folio(struct bio *, struct folio *, size_t len, size_t off); > extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *, > unsigned int, unsigned int); > int bio_add_zone_append_page(struct bio *bio, struct page *page, > -- > 2.30.2 >
On Thu, Jul 15, 2021 at 01:59:17PM -0700, Darrick J. Wong wrote: > On Thu, Jul 15, 2021 at 04:36:16AM +0100, Matthew Wilcox (Oracle) wrote: > > This is a thin wrapper around bio_add_page(). The main advantage here > > is the documentation that the submitter can expect to see folios in the > > completion handler, and that stupidly large folios are not supported. > > It's not currently possible to allocate stupidly large folios, but if > > it ever becomes possible, this function will fail gracefully instead of > > doing I/O to the wrong bytes. > > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > --- > > block/bio.c | 21 +++++++++++++++++++++ > > include/linux/bio.h | 3 ++- > > 2 files changed, 23 insertions(+), 1 deletion(-) > > > > diff --git a/block/bio.c b/block/bio.c > > index 1fab762e079b..1b500611d25c 100644 > > --- a/block/bio.c > > +++ b/block/bio.c > > @@ -933,6 +933,27 @@ int bio_add_page(struct bio *bio, struct page *page, > > } > > EXPORT_SYMBOL(bio_add_page); > > > > +/** > > + * bio_add_folio - Attempt to add part of a folio to a bio. > > + * @bio: Bio to add to. > > + * @folio: Folio to add. > > + * @len: How many bytes from the folio to add. > > + * @off: First byte in this folio to add. > > + * > > + * Always uses the head page of the folio in the bio. If a submitter > > + * only uses bio_add_folio(), it can count on never seeing tail pages > > + * in the completion routine. BIOs do not support folios larger than 2GiB. > > + * > > + * Return: The number of bytes from this folio added to the bio. > > + */ > > +size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len, > > + size_t off) > > +{ > > + if (len > UINT_MAX || off > UINT_MAX) > > Er... if bios don't support folios larger than 2GB, then why check @off > and @len against UINT_MAX, which is ~4GB? I suppose that's mostly a documentation problem. The limit is: struct bio_vec { struct page *bv_page; unsigned int bv_len; unsigned int bv_offset; }; so we can support folios which are 2GB in size (0x8000'0000) bytes, but if (theoretically, some day) we had a 4GB folio, we wouldn't be able to handle it in a single bio_vec. So there isn't anything between a 2GB folio and a 4GB folio; a 4GB folio isn't allowed and a 2GB one is. I don't think anything's wrong here, but maybe things could be worded better?
diff --git a/block/bio.c b/block/bio.c index 1fab762e079b..1b500611d25c 100644 --- a/block/bio.c +++ b/block/bio.c @@ -933,6 +933,27 @@ int bio_add_page(struct bio *bio, struct page *page, } EXPORT_SYMBOL(bio_add_page); +/** + * bio_add_folio - Attempt to add part of a folio to a bio. + * @bio: Bio to add to. + * @folio: Folio to add. + * @len: How many bytes from the folio to add. + * @off: First byte in this folio to add. + * + * Always uses the head page of the folio in the bio. If a submitter + * only uses bio_add_folio(), it can count on never seeing tail pages + * in the completion routine. BIOs do not support folios larger than 2GiB. + * + * Return: The number of bytes from this folio added to the bio. + */ +size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len, + size_t off) +{ + if (len > UINT_MAX || off > UINT_MAX) + return 0; + return bio_add_page(bio, &folio->page, len, off); +} + void bio_release_pages(struct bio *bio, bool mark_dirty) { struct bvec_iter_all iter_all; diff --git a/include/linux/bio.h b/include/linux/bio.h index 2203b686e1f0..ade93e2de6a1 100644 --- a/include/linux/bio.h +++ b/include/linux/bio.h @@ -462,7 +462,8 @@ extern void bio_uninit(struct bio *); extern void bio_reset(struct bio *); void bio_chain(struct bio *, struct bio *); -extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int); +int bio_add_page(struct bio *, struct page *, unsigned len, unsigned off); +size_t bio_add_folio(struct bio *, struct folio *, size_t len, size_t off); extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *, unsigned int, unsigned int); int bio_add_zone_append_page(struct bio *bio, struct page *page,
This is a thin wrapper around bio_add_page(). The main advantage here is the documentation that the submitter can expect to see folios in the completion handler, and that stupidly large folios are not supported. It's not currently possible to allocate stupidly large folios, but if it ever becomes possible, this function will fail gracefully instead of doing I/O to the wrong bytes. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- block/bio.c | 21 +++++++++++++++++++++ include/linux/bio.h | 3 ++- 2 files changed, 23 insertions(+), 1 deletion(-)