linux-kernel - [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL

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Date:   Mon, 23 Jan 2023 17:30:07 +0000
From:   David Howells <dhowells@...hat.com>
To:     Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>
Cc:     David Howells <dhowells@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-mm@...ck.org
Subject: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down

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.

Signed-off-by: David Howells <dhowells@...hat.com>
cc: Al Viro <viro@...iv.linux.org.uk>
cc: Christoph Hellwig <hch@....de>
cc: Matthew Wilcox <willy@...radead.org>
cc: linux-fsdevel@...r.kernel.org
cc: linux-mm@...ck.org
---

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:
  *