| Message ID | 167391053207.2311931.16398133457201442907.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iov_iter: Improve page extraction (ref, pin or just list) | expand |
> Changes: > ======== > ver #6) > - Add back the function to indicate the cleanup mode. > - Drop the cleanup_mode return arg to iov_iter_extract_pages(). > - Pass FOLL_SOURCE/DEST_BUF in gup_flags. Check this against the iter > data_source. FYI, the changelog goes after the --- so that it doesn't get added to the git history. > Link: https://lore.kernel.org/r/166732025748.3186319.8314014902727092626.stgit@warthog.procyon.org.uk/ # rfc > Link: https://lore.kernel.org/r/166869689451.3723671.18242195992447653092.stgit@warthog.procyon.org.uk/ # rfc > Link: https://lore.kernel.org/r/166920903885.1461876.692029808682876184.stgit@warthog.procyon.org.uk/ # v2 > Link: https://lore.kernel.org/r/166997421646.9475.14837976344157464997.stgit@warthog.procyon.org.uk/ # v3 > Link: https://lore.kernel.org/r/167305163883.1521586.10777155475378874823.stgit@warthog.procyon.org.uk/ # v4 > Link: https://lore.kernel.org/r/167344728530.2425628.9613910866466387722.stgit@warthog.procyon.org.uk/ # v5 And all these links aren't exactly useful. This fairly trivial commit is going to look like a hot mess in git. > +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages, > + size_t maxsize, unsigned int maxpages, > + unsigned int gup_flags, size_t *offset0); This function isn't actually added in the current patch. > +#define iov_iter_extract_mode(iter, gup_flags) \ > + (user_backed_iter(iter) ? \ > + (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ? \ > + FOLL_GET : FOLL_PIN : 0) And inline function would be nice here. I guess that would require moving the FULL flags into mm_types.h, though.
Christoph Hellwig <hch@infradead.org> wrote: > > +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages, > > + size_t maxsize, unsigned int maxpages, > > + unsigned int gup_flags, size_t *offset0); > > This function isn't actually added in the current patch. Oh... It ended up in the wrong patch. > > +#define iov_iter_extract_mode(iter, gup_flags) \ > > + (user_backed_iter(iter) ? \ > > + (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ? \ > > + FOLL_GET : FOLL_PIN : 0) > > And inline function would be nice here. I guess that would require > moving the FULL flags into mm_types.h, though. Yeah, the movement of FOLL_* flags is queued in a patch in akpm's tree. David
diff --git a/include/linux/uio.h b/include/linux/uio.h index 18b64068cc6d..38607c82e0cc 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -373,4 +373,32 @@ static inline void iov_iter_ubuf(struct iov_iter *i, enum iter_dir direction, }; } +ssize_t iov_iter_extract_pages(struct iov_iter *i, struct page ***pages, + size_t maxsize, unsigned int maxpages, + unsigned int gup_flags, size_t *offset0); + +/** + * iov_iter_extract_mode - Indicate how pages from the iterator will be retained + * @iter: The iterator + * @gup_flags: How the iterator is to be used (FOLL_SOURCE/DEST_BUF) + * + * Examine the iterator and the gup_flags and indicate by returning FOLL_PIN, + * FOLL_GET or 0 as to how, if at all, pages extracted from the iterator will + * be retained by the extraction function. + * + * FOLL_GET indicates that the pages will have a reference taken on them that + * the caller must put. This can be done for DMA/async DIO write from a page. + * + * FOLL_PIN indicates that the pages will have a pin placed in them that the + * caller must unpin. This is must be done for DMA/async DIO read to a page to + * avoid CoW problems in fork. + * + * 0 indicates that no measures are taken and that it's up to the caller to + * retain the pages. + */ +#define iov_iter_extract_mode(iter, gup_flags) \ + (user_backed_iter(iter) ? \ + (gup_flags & FOLL_BUF_MASK) == FOLL_SOURCE_BUF ? \ + FOLL_GET : FOLL_PIN : 0) + #endif
Add a function, iov_iter_extract_pages(), to extract a list of pages from an iterator. The pages may be returned with a reference added or a pin added or neither, depending on the type of iterator and the direction of transfer. The caller should pass FOLL_SOURCE_BUF or FOLL_DEST_BUF as part of gup_flags to indicate how the iterator contents are to be used. Add a second function, iov_iter_extract_mode(), to determine how the cleanup should be done. There are three cases: (1) Transfer *into* an ITER_IOVEC or ITER_UBUF iterator. Extracted pages will have pins obtained on them (but not references) so that fork() doesn't CoW the pages incorrectly whilst the I/O is in progress. iov_iter_extract_mode() will return FOLL_PIN for this case. The caller should use something like unpin_user_page() to dispose of the page. (2) Transfer is *out of* an ITER_IOVEC or ITER_UBUF iterator. Extracted pages will have references obtained on them, but not pins. iov_iter_extract_mode() will return FOLL_GET. The caller should use something like put_page() for page disposal. (3) Any other sort of iterator. No refs or pins are obtained on the page, the assumption is made that the caller will manage page retention. iov_iter_extract_mode() will return 0. The pages don't need additional disposal. Changes: ======== ver #6) - Add back the function to indicate the cleanup mode. - Drop the cleanup_mode return arg to iov_iter_extract_pages(). - Pass FOLL_SOURCE/DEST_BUF in gup_flags. Check this against the iter data_source. ver #4) - Use ITER_SOURCE/DEST instead of WRITE/READ. - Allow additional FOLL_* flags, such as FOLL_PCI_P2PDMA to be passed in. ver #3) - Switch to using EXPORT_SYMBOL_GPL to prevent indirect 3rd-party access to get/pin_user_pages_fast()[1]. Signed-off-by: David Howells <dhowells@redhat.com> cc: Al Viro <viro@zeniv.linux.org.uk> cc: Christoph Hellwig <hch@lst.de> cc: John Hubbard <jhubbard@nvidia.com> cc: Matthew Wilcox <willy@infradead.org> cc: linux-fsdevel@vger.kernel.org cc: linux-mm@kvack.org Link: https://lore.kernel.org/r/Y3zFzdWnWlEJ8X8/@infradead.org/ [1] Link: https://lore.kernel.org/r/166722777971.2555743.12953624861046741424.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166732025748.3186319.8314014902727092626.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166869689451.3723671.18242195992447653092.stgit@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/166920903885.1461876.692029808682876184.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/166997421646.9475.14837976344157464997.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/167305163883.1521586.10777155475378874823.stgit@warthog.procyon.org.uk/ # v4 Link: https://lore.kernel.org/r/167344728530.2425628.9613910866466387722.stgit@warthog.procyon.org.uk/ # v5 --- include/linux/uio.h | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+)