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From:   David Howells <dhowells@redhat.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     dhowells@redhat.com, Matthew Wilcox <willy@infradead.org>,
        John Hubbard <jhubbard@nvidia.com>,
        Christoph Hellwig <hch@lst.de>,
        Jeff Layton <jlayton@kernel.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] mm: Move FOLL_* defs to mm_types.h
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Content-ID: <2161257.1671657894.1@warthog.procyon.org.uk>
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Date:   Wed, 21 Dec 2022 21:24:54 +0000
Message-ID: <2161258.1671657894@warthog.procyon.org.uk>
Precedence: bulk

Hi Andrew,

Is it too late to ask you to add this to the current merge window?  It jus=
t
moves the FOLL_* flags between headers, flipping the order of the banner
comment and the defs.

It did have the following attributions:

	Reviewed-by: John Hubbard <jhubbard@nvidia.com>
	Reviewed-by: Christoph Hellwig <hch@lst.de>

but the FOLL_* flagset got altered during the merge window, so I redid the
patch.

Thanks,
David
---
mm: Move FOLL_* defs to mm_types.h
    =

Move FOLL_* definitions to linux/mm_types.h to make them more accessible
without having to drag in all of linux/mm.h and everything that drags in
too[1].

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: John Hubbard <jhubbard@nvidia.com>
cc: Christoph Hellwig <hch@lst.de>
cc: Matthew Wilcox <willy@infradead.org>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/linux-fsdevel/Y1%2FhSO+7kAJhGShG@casper.infr=
adead.org/ [1]
Link: https://lore.kernel.org/r/166732025009.3186319.3402781784409891214.s=
tgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166869688542.3723671.10243929000823258622.=
stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166920902968.1461876.15991975556984309489.=
stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/166997420723.9475.3907844523056304049.stgi=
t@warthog.procyon.org.uk/ # v3
---
 include/linux/mm.h       |   75 -----------------------------------------=
------
 include/linux/mm_types.h |   75 +++++++++++++++++++++++++++++++++++++++++=
++++++
 2 files changed, 75 insertions(+), 75 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f3f196e4d66d..be5edc0770ea 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3071,81 +3071,6 @@ static inline vm_fault_t vmf_error(int err)
 struct page *follow_page(struct vm_area_struct *vma, unsigned long addres=
s,
 			 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
-				 * 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 belo=
w */
-#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 sig=
nals */
-
-/*
- * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with ea=
ch
- * other. Here is what they mean, and how to use them:
- *
- * FOLL_LONGTERM indicates that the page will be held for an indefinite t=
ime
- * period _often_ under userspace control.  This is in contrast to
- * iov_iter_get_pages(), whose usages are transient.
- *
- * FIXME: For pages which are part of a filesystem, mappings are subject =
to the
- * lifetime enforced by the filesystem and we need guarantees that longte=
rm
- * users like RDMA and V4L2 only establish mappings which coordinate usag=
e with
- * the filesystem.  Ideas for this coordination include revoking the long=
term
- * pin, delaying writeback, bounce buffer page writeback, etc.  As FS DAX=
 was
- * added after the problem with filesystems was found FS DAX VMAs are
- * specifically failed.  Filesystem pages are still subject to bugs and u=
se of
- * FOLL_LONGTERM should be avoided on those pages.
- *
- * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call=
.
- * Currently only get_user_pages() and get_user_pages_fast() support this=
 flag
- * and calls to get_user_pages_[un]locked are specifically not allowed.  =
This
- * is due to an incompatibility with the FS DAX check and
- * FAULT_FLAG_ALLOW_RETRY.
- *
- * In the CMA case: long term pins in a CMA region would unnecessarily fr=
agment
- * that region.  And so, CMA attempts to migrate the page before pinning,=
 when
- * FOLL_LONGTERM is specified.
- *
- * FOLL_PIN indicates that a special kind of tracking (not just page->_re=
fcount,
- * but an additional pin counting system) will be invoked. This is intend=
ed for
- * anything that gets a page reference and then touches page data (for ex=
ample,
- * Direct IO). This lets the filesystem know that some non-file-system en=
tity is
- * potentially changing the pages' data. In contrast to FOLL_GET (whose p=
ages
- * are released via put_page()), FOLL_PIN pages must be released, ultimat=
ely, by
- * a call to unpin_user_page().
- *
- * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use dif=
ferent
- * and separate refcounting mechanisms, however, and that means that each=
 has
- * its own acquire and release mechanisms:
- *
- *     FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
- *
- *     FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to re=
lease.
- *
- * FOLL_PIN and FOLL_GET are mutually exclusive for a given function call=
.
- * (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-=
based
- * calls applied to them, and that's perfectly OK. This is a constraint o=
n the
- * callers, not on the pages.)
- *
- * FOLL_PIN should be set internally by the pin_user_pages*() APIs, never
- * directly by the caller. That's in order to help avoid mismatches when
- * releasing pages: get_user_pages*() pages must be released via put_page=
(),
- * while pin_user_pages*() pages must be released via unpin_user_page().
- *
- * Please see Documentation/core-api/pin_user_pages.rst for more informat=
ion.
- */
-
 static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
 {
 	if (vm_fault & VM_FAULT_OOM)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 3b8475007734..4e1031626403 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1085,4 +1085,79 @@ enum fault_flag {
 =

 typedef unsigned int __bitwise zap_flags_t;
 =

+/*
+ * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with ea=
ch
+ * other. Here is what they mean, and how to use them:
+ *
+ * FOLL_LONGTERM indicates that the page will be held for an indefinite t=
ime
+ * period _often_ under userspace control.  This is in contrast to
+ * iov_iter_get_pages(), whose usages are transient.
+ *
+ * FIXME: For pages which are part of a filesystem, mappings are subject =
to the
+ * lifetime enforced by the filesystem and we need guarantees that longte=
rm
+ * users like RDMA and V4L2 only establish mappings which coordinate usag=
e with
+ * the filesystem.  Ideas for this coordination include revoking the long=
term
+ * pin, delaying writeback, bounce buffer page writeback, etc.  As FS DAX=
 was
+ * added after the problem with filesystems was found FS DAX VMAs are
+ * specifically failed.  Filesystem pages are still subject to bugs and u=
se of
+ * FOLL_LONGTERM should be avoided on those pages.
+ *
+ * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call=
.
+ * Currently only get_user_pages() and get_user_pages_fast() support this=
 flag
+ * and calls to get_user_pages_[un]locked are specifically not allowed.  =
This
+ * is due to an incompatibility with the FS DAX check and
+ * FAULT_FLAG_ALLOW_RETRY.
+ *
+ * In the CMA case: long term pins in a CMA region would unnecessarily fr=
agment
+ * that region.  And so, CMA attempts to migrate the page before pinning,=
 when
+ * FOLL_LONGTERM is specified.
+ *
+ * FOLL_PIN indicates that a special kind of tracking (not just page->_re=
fcount,
+ * but an additional pin counting system) will be invoked. This is intend=
ed for
+ * anything that gets a page reference and then touches page data (for ex=
ample,
+ * Direct IO). This lets the filesystem know that some non-file-system en=
tity is
+ * potentially changing the pages' data. In contrast to FOLL_GET (whose p=
ages
+ * are released via put_page()), FOLL_PIN pages must be released, ultimat=
ely, by
+ * a call to unpin_user_page().
+ *
+ * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use dif=
ferent
+ * and separate refcounting mechanisms, however, and that means that each=
 has
+ * its own acquire and release mechanisms:
+ *
+ *     FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
+ *
+ *     FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to re=
lease.
+ *
+ * FOLL_PIN and FOLL_GET are mutually exclusive for a given function call=
.
+ * (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-=
based
+ * calls applied to them, and that's perfectly OK. This is a constraint o=
n the
+ * callers, not on the pages.)
+ *
+ * FOLL_PIN should be set internally by the pin_user_pages*() APIs, never
+ * directly by the caller. That's in order to help avoid mismatches when
+ * releasing pages: get_user_pages*() pages must be released via put_page=
(),
+ * while pin_user_pages*() pages must be released via unpin_user_page().
+ *
+ * Please see Documentation/core-api/pin_user_pages.rst for more informat=
ion.
+ */
+
+#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
+				 * 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 belo=
w */
+#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 sig=
nals */
+
 #endif /* _LINUX_MM_TYPES_H */