From: Wei Yang <richard.weiyang@gmail.com>
To: Dev Jain <dev.jain@arm.com>
Cc: akpm@linux-foundation.org, david@kernel.org,
lorenzo.stoakes@oracle.com, ziy@nvidia.com,
baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com,
npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org,
lance.yang@linux.dev, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] khugepaged: remove redundant index check for pmd-folios
Date: Wed, 4 Mar 2026 08:27:35 +0000 [thread overview]
Message-ID: <20260304082735.j4brgesse3vp34rz@master> (raw)
In-Reply-To: <20260227143501.1488110-1-dev.jain@arm.com>
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)
This is because __filemap_add_folio() align the index to folio_order(), right?
>
>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 <dev.jain@arm.com>
--
Wei Yang
Help you, Help me
next prev parent reply other threads:[~2026-03-04 8:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-27 14:35 Dev Jain
2026-02-27 20:57 ` David Hildenbrand (Arm)
2026-02-28 4:44 ` Lance Yang
2026-03-03 2:16 ` Baolin Wang
2026-03-03 9:56 ` Lorenzo Stoakes
2026-03-04 8:27 ` Wei Yang [this message]
2026-03-04 8:44 ` Dev Jain
2026-03-04 9:22 ` Anshuman Khandual
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