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mm/huge_memory: try avoiding write faults when changing PMD protection 

Let's replicate what we have for PTEs in can_change_pte_writable() also
for PMDs.

While this might look like a pure performance improvement, we'll us this to
get rid of savedwrite handling in do_huge_pmd_numa_page() next. Place
do_huge_pmd_numa_page() strategically good for that purpose.

Note that MM_CP_TRY_CHANGE_WRITABLE is currently only set when we come
via mprotect_fixup().

Link: https://lkml.kernel.org/r/20221108174652.198904-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-11-08 18:46:48 +01:00 committed by Andrew Morton
parent 7ea7e33384
commit c27f479ef5
1 changed files with 36 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
mm/huge_memory.c
View File

@ -1390,6 +1390,36 @@ fallback:
return VM_FAULT_FALLBACK;
}
static inline bool can_change_pmd_writable(struct vm_area_struct *vma,
unsigned long addr, pmd_t pmd)
{
struct page *page;
if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE)))
return false;
/* Don't touch entries that are not even readable (NUMA hinting). */
if (pmd_protnone(pmd))
return false;
/* Do we need write faults for softdirty tracking? */
if (vma_soft_dirty_enabled(vma) && !pmd_soft_dirty(pmd))
return false;
/* Do we need write faults for uffd-wp tracking? */
if (userfaultfd_huge_pmd_wp(vma, pmd))
return false;
if (!(vma->vm_flags & VM_SHARED)) {
/* See can_change_pte_writable(). */
page = vm_normal_page_pmd(vma, addr, pmd);
return page && PageAnon(page) && PageAnonExclusive(page);
}
/* See can_change_pte_writable(). */
return pmd_dirty(pmd);
}
/* FOLL_FORCE can write to even unwritable PMDs in COW mappings. */
static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page,
struct vm_area_struct *vma,
@ -1893,13 +1923,17 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
*/
entry = pmd_clear_uffd_wp(entry);
}
/* See change_pte_range(). */
if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && !pmd_write(entry) &&
can_change_pmd_writable(vma, addr, entry))
entry = pmd_mkwrite(entry);
ret = HPAGE_PMD_NR;
set_pmd_at(mm, addr, pmd, entry);
if (huge_pmd_needs_flush(oldpmd, entry))
tlb_flush_pmd_range(tlb, addr, HPAGE_PMD_SIZE);
BUG_ON(vma_is_anonymous(vma) && !preserve_write && pmd_write(entry));
unlock:
spin_unlock(ptl);
return ret;