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| author | Dev Jain <dev.jain@arm.com> | 2026-02-27 17:35:01 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-04-05 23:53:10 +0300 |
| commit | 22aa3321992eee0a39fb465e5083f5b8b5e7a82a (patch) | |
| tree | 4edf51ffab6b39bba39c9fe445fa513568943ff1 | |
| parent | 1745ccbd2907db2bdaa843e4abccde4fdaccbe5d (diff) | |
| download | linux-22aa3321992eee0a39fb465e5083f5b8b5e7a82a.tar.xz | |
khugepaged: remove redundant index check for pmd-folios
Claim: folio_order(folio) == HPAGE_PMD_ORDER => folio->index == start.
Proof: Both loops in hpage_collapse_scan_file and collapse_file, which
iterate on the xarray, have the invariant that start <= folio->index <
start + HPAGE_PMD_NR ... (i)
A folio is always naturally aligned in the pagecache, therefore
folio_order == HPAGE_PMD_ORDER => IS_ALIGNED(folio->index, HPAGE_PMD_NR) == true ... (ii)
thp_vma_allowable_order -> thp_vma_suitable_order requires that the virtual
offsets in the VMA are aligned to the order,
=> IS_ALIGNED(start, HPAGE_PMD_NR) == true ... (iii)
Combining (i), (ii) and (iii), the claim is proven.
Therefore, remove this check.
While at it, simplify the comments.
Link: https://lkml.kernel.org/r/20260227143501.1488110-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/khugepaged.c | 14 |
1 files changed, 4 insertions, 10 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 13b0fe50dfc5..ab97423fe837 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2023,9 +2023,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, * we locked the first folio, then a THP might be there already. * This will be discovered on the first iteration. */ - if (folio_order(folio) == HPAGE_PMD_ORDER && - folio->index == start) { - /* Maybe PMD-mapped */ + if (folio_order(folio) == HPAGE_PMD_ORDER) { result = SCAN_PTE_MAPPED_HUGEPAGE; goto out_unlock; } @@ -2353,15 +2351,11 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, continue; } - if (folio_order(folio) == HPAGE_PMD_ORDER && - folio->index == start) { - /* Maybe PMD-mapped */ + if (folio_order(folio) == HPAGE_PMD_ORDER) { result = SCAN_PTE_MAPPED_HUGEPAGE; /* - * For SCAN_PTE_MAPPED_HUGEPAGE, further processing - * by the caller won't touch the page cache, and so - * it's safe to skip LRU and refcount checks before - * returning. + * PMD-sized THP implies that we can only try + * retracting the PTE table. */ folio_put(folio); break; |