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Code Activity

mm: mempolicy: keep VMA walk if both MPOL_MF_STRICT and MPOL_MF_MOVE are specified

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When calling mbind() with MPOL_MF_{MOVE|MOVEALL} | MPOL_MF_STRICT, kernel
should attempt to migrate all existing pages, and return -EIO if there is
misplaced or unmovable page.  Then commit 6f4576e368 ("mempolicy: apply
page table walker on queue_pages_range()") messed up the return value and
didn't break VMA scan early ianymore when MPOL_MF_STRICT alone.  The
return value problem was fixed by commit a7f40cfe3b ("mm: mempolicy:
make mbind() return -EIO when MPOL_MF_STRICT is specified"), but it broke
the VMA walk early if unmovable page is met, it may cause some pages are
not migrated as expected.

The code should conceptually do:

 if (MPOL_MF_MOVE|MOVEALL)
     scan all vmas
     try to migrate the existing pages
     return success
 else if (MPOL_MF_MOVE* | MPOL_MF_STRICT)
     scan all vmas
     try to migrate the existing pages
     return -EIO if unmovable or migration failed
 else /* MPOL_MF_STRICT alone */
     break early if meets unmovable and don't call mbind_range() at all
 else /* none of those flags */
     check the ranges in test_walk, EFAULT without mbind_range() if discontig.

Fixed the behavior.

Link: https://lkml.kernel.org/r/20230920223242.3425775-1-yang@os.amperecomputing.com
Fixes: a7f40cfe3b ("mm: mempolicy: make mbind() return -EIO when MPOL_MF_STRICT is specified")
Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: David Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>	[4.9+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yang Shi 2023-09-20 15:32:42 -07:00 • committed by Andrew Morton
parent 45120b1574
commit 24526268f4
1 changed files with 19 additions and 20 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

39
mm/mempolicy.c
View file

@ -426,6 +426,7 @@ struct queue_pages {
unsigned long start;
unsigned long end;
struct vm_area_struct *first;
bool has_unmovable;
};
/*
@ -446,9 +447,8 @@ static inline bool queue_folio_required(struct folio *folio,
/*
* queue_folios_pmd() has three possible return values:
* 0 - folios are placed on the right node or queued successfully, or
* special page is met, i.e. huge zero page.
* 1 - there is unmovable folio, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
* specified.
* special page is met, i.e. zero page, or unmovable page is found
* but continue walking (indicated by queue_pages.has_unmovable).
* -EIO - is migration entry or only MPOL_MF_STRICT was specified and an
* existing folio was already on a node that does not follow the
* policy.
@ -479,7 +479,7 @@ static int queue_folios_pmd(pmd_t *pmd, spinlock_t *ptl, unsigned long addr,
if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
if (!vma_migratable(walk->vma) ||
migrate_folio_add(folio, qp->pagelist, flags)) {
ret = 1;
qp->has_unmovable = true;
goto unlock;
}
} else
@ -495,9 +495,8 @@ unlock:
*
* queue_folios_pte_range() has three possible return values:
* 0 - folios are placed on the right node or queued successfully, or
* special page is met, i.e. zero page.
* 1 - there is unmovable folio, and MPOL_MF_MOVE* & MPOL_MF_STRICT were
* specified.
* special page is met, i.e. zero page, or unmovable page is found
* but continue walking (indicated by queue_pages.has_unmovable).
* -EIO - only MPOL_MF_STRICT was specified and an existing folio was already
* on a node that does not follow the policy.
*/
@ -508,7 +507,6 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
struct folio *folio;
struct queue_pages *qp = walk->private;
unsigned long flags = qp->flags;
bool has_unmovable = false;
pte_t *pte, *mapped_pte;
pte_t ptent;
spinlock_t *ptl;
@ -538,11 +536,12 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
if (!queue_folio_required(folio, qp))
continue;
if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
/* MPOL_MF_STRICT must be specified if we get here */
if (!vma_migratable(vma)) {
has_unmovable = true;
break;
}
/*
* MPOL_MF_STRICT must be specified if we get here.
* Continue walking vmas due to MPOL_MF_MOVE* flags.
*/
if (!vma_migratable(vma))
qp->has_unmovable = true;
/*
* Do not abort immediately since there may be
@ -550,16 +549,13 @@ static int queue_folios_pte_range(pmd_t *pmd, unsigned long addr,
* need migrate other LRU pages.
*/
if (migrate_folio_add(folio, qp->pagelist, flags))
has_unmovable = true;
qp->has_unmovable = true;
} else
break;
}
pte_unmap_unlock(mapped_pte, ptl);
cond_resched();
if (has_unmovable)
return 1;
return addr != end ? -EIO : 0;
}
@ -599,7 +595,7 @@ static int queue_folios_hugetlb(pte_t *pte, unsigned long hmask,
* Detecting misplaced folio but allow migrating folios which
* have been queued.
*/
ret = 1;
qp->has_unmovable = true;
goto unlock;
}
@ -620,7 +616,7 @@ static int queue_folios_hugetlb(pte_t *pte, unsigned long hmask,
* Failed to isolate folio but allow migrating pages
* which have been queued.
*/
ret = 1;
qp->has_unmovable = true;
}
unlock:
spin_unlock(ptl);
@ -756,12 +752,15 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
.start = start,
.end = end,
.first = NULL,
.has_unmovable = false,
};
const struct mm_walk_ops *ops = lock_vma ?
&queue_pages_lock_vma_walk_ops : &queue_pages_walk_ops;
err = walk_page_range(mm, start, end, ops, &qp);
if (qp.has_unmovable)
err = 1;
if (!qp.first)
/* whole range in hole */
err = -EFAULT;
@ -1358,7 +1357,7 @@ static long do_mbind(unsigned long start, unsigned long len,
putback_movable_pages(&pagelist);
}
if ((ret > 0) || (nr_failed && (flags & MPOL_MF_STRICT)))
if (((ret > 0) || nr_failed) && (flags & MPOL_MF_STRICT))
err = -EIO;
} else {
up_out: