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U2FsdGVkX19+WX4SN59cmf8TM8w3zgY6qJhI3KXGaQ32/Ss1mABSV6HanF2BFHlcjjAO9NQ2k/J/eigPPYdPEOMR7HR1eDSXXOzg/rOVz46yG2PDfBnZiw1Nbd9HHQUiAy4k5D3jN7DMX8erOmSb2KSPwVdVaWss2EvcKtdDw+peAW0fg/J5W3qjWTobblmrfbRUa9q6V2LtyfXPZaDlbkE3kf1zZc+aG/+8BUDRHVonp/AtRt2yfvV5P7YMCVH/XEk8fn88nakGYW7YHNNPu9mnNy9KWu7DOIPg6CEqL63pvMzP8vJlUtxldQEUizsiqCmJez6hTWa03v7UyPse0xRFihLJalc/mmA0X1dCHIZgXevToAC9yTmBxv1MfJCoIgEM4FkuvxzEIYvdwlaJwXWxEd3Q99h2JYjK1uyPkVUBFTJ6UXIbTq39g2GsJjCxmQDgCIs+NfHlUQW8EsrsEuRbchLuBzxWvZ43BHb7pkmziPyWCkbMVhP3CaeQsbYnd0aV6Odp09YIjjMgj9OB0trdaEcPphrTiHA0YwWBFQ9EMVSz5FQuGhyamO0d9ANK4Ps0GhotLxaM52NnJrTza3B438LbfFekQ8pa/lwUk3AjzInhUjgSmWXtPlCUNQK6ElSObyhOfZJQ2lBBM2hmKjhtQtvJCroqfVYc6BoCRy7RyiIztaIHdfsF0EQWeKhJhVk4obgValBEzl8m7AyaSFy5zjM6X+LnnQcR+W1+E/jOw/uAEttHpCCpxLYePBNKN2P9dDdew8zUvwzlppwQ0OKN5hRGmb77K1j1OgUAzcYpIw8u6SUmbRy5Tc6IWBR+bHPCAVC9TpXVCNsF3MONAfJV2ZjzlRZKMyhqYBVEI772kqlQdus06Mrrl3ewnJId7F4DHkpjeC7R6naKyt04VtIQgEFVm5JDH/2tNCm/4esbGUczqv8UhN8doppNCYVRicN9E1CuF0SBJKP2G+7 Wvi65lgR 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Feb 27, 2026 at 08:05:01PM +0530, Dev Jain wrote: > 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. > > Signed-off-by: Dev Jain Very mathematical :) LGTM so: Reviewed-by: Lorenzo Stoakes > --- > v1->v2: > - Remove the check instead of converting to VM_WARN_ON > - While at it, simplify the comments > > Based on mm-new (8982358e1c87). > > mm/khugepaged.c | 14 ++++---------- > 1 file changed, 4 insertions(+), 10 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 5f668c1dd0fe4..b7b4680d27ab1 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2015,9 +2015,7 @@ 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; > } > @@ -2345,15 +2343,11 @@ 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; > -- > 2.34.1 >