linux-kernel - [PATCH v7 8/8] mm: Renumber FOLL_GET and FOLL

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Date:   Fri, 20 Jan 2023 17:55:56 +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 v7 8/8] mm: Renumber FOLL_GET and FOLL_PIN down

Renumber FOLL_GET and FOLL_PIN down to bit 0 and 1 respectively so that
they are coincidentally the same as BIO_PAGE_REFFED and BIO_PAGE_PINNED 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).

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
---
 include/linux/mm.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1cf8f4eb946..33c9eacd9548 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3074,12 +3074,13 @@ 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_GET	0x01	/* do get_page on page (equivalent to BIO_FOLL_GET) */
+#define FOLL_PIN	0x02	/* pages must be released via unpin_user_page */
+#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 */
@@ -3088,7 +3089,6 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
 #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 */