On 1/23/23 09:30, David Howells wrote:
Renumber FOLL_PIN and FOLL_GET down to bit 0 and 1 respectively so that
they are coincidentally the same as BIO_PAGE_PINNED and BIO_PAGE_REFFED and
also so that they can be stored in the bottom two bits of a page pointer
(something I'm looking at for zerocopy socket fragments).
(Note that BIO_PAGE_REFFED should probably be got rid of at some point,
hence why FOLL_PIN is at 0.)
Also renumber down the other FOLL_* flags to close the gaps.
Should we also get these sorted into internal-to-mm and public sets?
Because Jason (+Cc) again was about to split them apart into
mm/internal.h [1] and that might make that a little cleaner.
Also, I don't think that there is any large readability difference
either way between 0x and <<1, so whatever you and Christophe settle on
there seems fine.
So either way with those points,
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
thanks,
--
John Hubbard
NVIDIA
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx
---
Notes:
ver #8)
- Put FOLL_PIN at bit 0 and FOLL_GET at bit 1 to match BIO_PAGE_*.
- Renumber the remaining flags down to fill in the gap.
include/linux/mm.h | 32 +++++++++++++++++---------------
1 file changed, 17 insertions(+), 15 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3de9d88f8524..c95bc4f77e8f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3074,26 +3074,28 @@ static inline vm_fault_t vmf_error(int err)
struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
unsigned int foll_flags);
-#define FOLL_WRITE 0x01 /* check pte is writable */
-#define FOLL_TOUCH 0x02 /* mark page accessed */
-#define FOLL_GET 0x04 /* do get_page on page */
-#define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
-#define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
-#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO
+#define FOLL_PIN 0x01 /* pages must be released via unpin_user_page */
+#define FOLL_GET 0x02 /* do get_page on page (equivalent to BIO_FOLL_GET) */
+#define FOLL_WRITE 0x04 /* check pte is writable */
+#define FOLL_TOUCH 0x08 /* mark page accessed */
+#define FOLL_DUMP 0x10 /* give error on hole if it would be zero */
+#define FOLL_FORCE 0x20 /* get_user_pages read/write w/o permission */
+#define FOLL_NOWAIT 0x40 /* if a disk transfer is needed, start the IO
* and return without waiting upon it */
#define FOLL_NOFAULT 0x80 /* do not fault in pages */
#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
-#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
-#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
-#define FOLL_ANON 0x8000 /* don't do file mappings */
-#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */
-#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
-#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */
-#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */
-#define FOLL_PCI_P2PDMA 0x100000 /* allow returning PCI P2PDMA pages */
-#define FOLL_INTERRUPTIBLE 0x200000 /* allow interrupts from generic signals */
+#define FOLL_TRIED 0x200 /* a retry, previous pass started an IO */
+#define FOLL_REMOTE 0x400 /* we are working on non-current tsk/mm */
+#define FOLL_ANON 0x800 /* don't do file mappings */
+#define FOLL_LONGTERM 0x1000 /* mapping lifetime is indefinite: see below */
+#define FOLL_SPLIT_PMD 0x2000 /* split huge pmd before returning */
+#define FOLL_FAST_ONLY 0x4000 /* gup_fast: prevent fall-back to slow gup */
+#define FOLL_PCI_P2PDMA 0x8000 /* allow returning PCI P2PDMA pages */
+#define FOLL_INTERRUPTIBLE 0x10000 /* allow interrupts from generic signals */
/*
+ * Note that FOLL_PIN is sorted to bit 0 to be coincident with BIO_PAGE_PINNED.
+ *
* FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
* other. Here is what they mean, and how to use them:
*
