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Thu, 10 Sep 2026 09:04:37 -0400 (EDT) Date: Thu, 10 Sep 2026 14:04:35 +0100 From: Kiryl Shutsemau To: Baolin Wang Cc: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, rppt@kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, usama.anjum@arm.com, usama.arif@linux.dev, nico.pache@linux.dev, ziy@nvidia.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, vbabka@kernel.org, agordeev@linux.ibm.com, jgg@ziepe.ca, leon@kernel.org, kernel-team@meta.com Subject: Re: [PATCH v5 08/19] selftests/mm: add folio-order check for address ranges Message-ID: References: <20260908125105.1510704-1-kirill@shutemov.name> <20260908125105.1510704-9-kirill@shutemov.name> <65bf1722-c1fd-452a-88c1-c030b042cfbc@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <65bf1722-c1fd-452a-88c1-c030b042cfbc@linux.alibaba.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 43122180002 X-Rspam-User: X-Stat-Signature: bk3q5pxado55f7r1gkaik4jgd8f78ymd X-HE-Tag: 1789045482-261079 X-HE-Meta: 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 aILaDtOR C0eeUw4E2D0DuBwxWwAeN7UnngD+vumYBIBTnkhiQm9z+C2CeALa5SSQfxf7kdkDMqFyvyrp03IjtmwYSNz7rcYU7BGTKeX4/rwhR1f/fBRS0zeSUGkoD43eJNupdqUt1GdIJb1qNm6vfNHOO4aBwfsYvQvERQ0hi479FykuXAg4fUYxQYLy27UNXo1pv6O633r4mtDAlRGVbxkWTKJDNTp5NF+bxmDQE2Q9z2AWOvxuctHHqJ82WiwdN+BvwC9SAgMRuWVd7s/qY8qt2/gz1I68vfj2npRI9LXbi62BDakuc1D7wC99Z1nZS+1YE87Z0Pw/ZI3hao9t6T+8FREB3LHcVJfcYVDEoRnPjFbwYRf91HjKT7jlOOXmvXQ4Sj5oR92lW2FJcWlkCPy91imHyoRYrPZbLi7JHT1dOOH9afqHUYcYYkceLoSTKOaZw9PjU0BXe0MVAZhDS61VPDFUXuvJ9Ig== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 10, 2026 at 07:14:42PM +0800, Baolin Wang wrote: > > > On 9/10/26 6:45 PM, Kiryl Shutsemau wrote: > > On Wed, Sep 09, 2026 at 06:01:13PM +0800, Baolin Wang wrote: > > > > > > > > > On 9/8/26 8:50 PM, Kiryl Shutsemau wrote: > > > > From: "Kiryl Shutsemau (Meta)" > > > > > > > > An mTHP collapse test needs to know that a range is backed by folios of the > > > > target order, and that they sit where a collapse would put them. Nothing > > > > answers that today: is_backed_by_folio() classifies the folio behind a > > > > single page, and check_huge_anon() reads smaps AnonHugePages, which only > > > > accounts PMD mappings. > > > > > > Have you checked check_large_folios() in vm_util.c? It seems to meet your > > > requirements, or am I missing something? > > > > The changelog is out of date, sorry: since 6dedaf0d46a9 check_huge_anon() > > counts mTHP folios through check_large_folios() rather than reading > > smaps, and it is what check_huge() already uses for mthp_khugepaged. > > > > It could do this job too, called once per window. > > > > What is_range_backed_by_order() adds is alignment check: the folio has > > to sit at the window start. And check_large_folios() reopens two fds per > > per call which kinda wasteful. > > OK. But can we extend the check_huge_xxx() functions to meet your > requirements, for example by adding a check_aligned_huge_xxx() that wraps > the underlying implementation of check_large_folios()? > > I still find it confusing that khugepaged.c has two separate sets of > functions for checking large folios. Agreed that two sets is one too many. Yeoreum's series rewrites check_huge_xxx() on top of pagemap and kpageflags, which is what is_backed_by_folio() already walks, so once that lands the two can meet: the mTHP branch of check_huge() checks each window for a folio of the order at its start, and is_range_backed_by_order() goes away or becomes its internal. That also makes the generic mTHP cases stricter for free. I would rather do that as a follow-up than fold it into either series now, since both touch the same functions. -- Kiryl Shutsemau / Kirill A. Shutemov