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Wed, 04 Mar 2026 00:27:35 -0800 (PST) Date: Wed, 4 Mar 2026 08:27:35 +0000 From: Wei Yang To: Dev Jain 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 Message-ID: <20260304082735.j4brgesse3vp34rz@master> Reply-To: Wei Yang References: <20260227143501.1488110-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260227143501.1488110-1-dev.jain@arm.com> User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Queue-Id: A143A140010 X-Rspamd-Server: rspam07 X-Stat-Signature: 58dry5q6ax847qpwkty4cekx5ohmzw96 X-Rspam-User: X-HE-Tag: 1772612858-84495 X-HE-Meta: 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 R9kVNgbE 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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) 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 -- Wei Yang Help you, Help me