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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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) 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