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mm/gup: replace FOLL_NUMA by gup_can_follow_protnone()

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Patch series "mm: minor cleanups around NUMA hinting".

Working on some GUP cleanups (e.g., getting rid of some FOLL_ flags) and
preparing for other GUP changes (getting rid of FOLL_FORCE|FOLL_WRITE for
for taking a R/O longterm pin), this is something I can easily send out
independently.

Get rid of FOLL_NUMA, allow FOLL_FORCE access to PROT_NONE mapped pages in
GUP-fast, and fixup some documentation around NUMA hinting.


This patch (of 3):

No need for a special flag that is not even properly documented to be
internal-only.

Let's just factor this check out and get rid of this flag.  The separate
function has the nice benefit that we can centralize comments.

Link: https://lkml.kernel.org/r/20220825164659.89824-2-david@redhat.com
Link: https://lkml.kernel.org/r/20220825164659.89824-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-08-25 18:46:57 +02:00 committed by Andrew Morton
parent f7091ed64e
commit 474098edac
3 changed files with 18 additions and 12 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

16
include/linux/mm.h
View file

@ -2933,7 +2933,6 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
* 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_NUMA 0x200 /* force NUMA hinting page fault */
#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
#define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */
#define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */
@ -3054,6 +3053,21 @@ static inline bool gup_must_unshare(unsigned int flags, struct page *page)
return !PageAnonExclusive(page);
}
/*
* Indicates whether GUP can follow a PROT_NONE mapped page, or whether
* a (NUMA hinting) fault is required.
*/
static inline bool gup_can_follow_protnone(unsigned int flags)
{
/*
* FOLL_FORCE has to be able to make progress even if the VMA is
* inaccessible. Further, FOLL_FORCE access usually does not represent
* application behaviour and we should avoid triggering NUMA hinting
* faults.
*/
return flags & FOLL_FORCE;
}
typedef int (*pte_fn_t)(pte_t *pte, unsigned long addr, void *data);
extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
unsigned long size, pte_fn_t fn, void *data);

12
mm/gup.c
View file

@ -561,7 +561,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
migration_entry_wait(mm, pmd, address);
goto retry;
}
if ((flags & FOLL_NUMA) && pte_protnone(pte))
if (pte_protnone(pte) && !gup_can_follow_protnone(flags))
goto no_page;
page = vm_normal_page(vma, address, pte);
@ -714,7 +714,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
if (likely(!pmd_trans_huge(pmdval)))
return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
if ((flags & FOLL_NUMA) && pmd_protnone(pmdval))
if (pmd_protnone(pmdval) && !gup_can_follow_protnone(flags))
return no_page_table(vma, flags);
retry_locked:
@ -1160,14 +1160,6 @@ static long __get_user_pages(struct mm_struct *mm,
VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
/*
* If FOLL_FORCE is set then do not force a full fault as the hinting
* fault information is unrelated to the reference behaviour of a task
* using the address space
*/
if (!(gup_flags & FOLL_FORCE))
gup_flags |= FOLL_NUMA;
do {
struct page *page;
unsigned int foll_flags = gup_flags;

2
mm/huge_memory.c
View file

@ -1447,7 +1447,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
return ERR_PTR(-EFAULT);
/* Full NUMA hinting faults to serialise migration in fault paths */
if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
if (pmd_protnone(*pmd) && !gup_can_follow_protnone(flags))
return NULL;
if (!pmd_write(*pmd) && gup_must_unshare(flags, page))