From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Dev Jain <dev.jain@arm.com>,
akpm@linux-foundation.org, lorenzo.stoakes@oracle.com
Cc: 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: Fri, 27 Feb 2026 21:57:01 +0100 [thread overview]
Message-ID: <4f512562-1fed-454e-aca3-2e1a257c28b0@kernel.org> (raw)
In-Reply-To: <20260227143501.1488110-1-dev.jain@arm.com>
On 2/27/26 15:35, 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 <dev.jain@arm.com>
> ---
There might be some conflict with Nicos changes.
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
--
Cheers,
David
prev parent reply other threads:[~2026-02-27 20:57 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-27 14:35 Dev Jain
2026-02-27 20:57 ` David Hildenbrand (Arm) [this message]
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