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Wed, 21 Oct 2026 06:32:30 -0400 (EDT) Date: Wed, 21 Oct 2026 11:32:29 +0100 From: Kiryl Shutsemau To: Zenghui Yu Cc: Andrew Morton , "David Hildenbrand (Arm)" , "Lorenzo Stoakes (ARM)" , Mike Rapoport , Baolin Wang , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Muhammad Usama Anjum , Usama Arif , "Nico Pache (Red Hat)" , Zi Yan , Barry Song , Dev Jain , Hugh Dickins , Lance Yang , "Liam R. Howlett" , Michal Hocko , Ryan Roberts , Shuah Khan , Suren Baghdasaryan , "Vlastimil Babka (SUSE)" , Alexander Gordeev , Jason Gunthorpe , Leon Romanovsky , kernel-team@meta.com Subject: Re: [PATCH v6 02/19] selftests/mm: skip collapse_compound_extreme() where the PMD is too large Message-ID: References: <20260919002451.496763-1-kirill@shutemov.name> <20260919002451.496763-3-kirill@shutemov.name> <5862cddb-a78f-419f-a5a1-15e16a422bf5@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5862cddb-a78f-419f-a5a1-15e16a422bf5@linux.dev> X-Rspamd-Queue-Id: 1C6FC40002 X-Rspam-User: X-Stat-Signature: 1sig5uh8sht4eepzige6ad4n971hwphc X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1792578754-76068 X-HE-Meta: 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 XeVSrknz 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu, Oct 08, 2026 at 07:52:18PM +0800, Zenghui Yu wrote: > Hi Kiryl, > > On 9/19/26 8:24 AM, Kiryl Shutsemau wrote: > > From: "Kiryl Shutsemau (Meta)" > > > > collapse_compound_extreme() builds a PTE table full of distinct PTE-mapped > > compound pages by cycling hpage_pmd_nr fault-time THPs through mremap. It > > therefore needs hpage_pmd_nr PMD-order allocations in a row. That is fine > > at a 2M PMD (4K base pages) or a 32M one (16K). A 512M PMD -- arm64 with > > 64K base pages -- makes each of those an order-13 allocation, which the > > allocator cannot reliably hand out even once, let alone 8192 times. > > > > The failure is not a quiet one: the case calls ksft_exit_fail_msg(), so the > > whole binary stops and every case after it is lost. > > > > Skip the case where the PMD is larger than 32M. The MADV_COLLAPSE cases > > still cover PMD-order collapse on those configurations, and 4K and 16K > > PMDs are unaffected. > > collapse_compound_extreme() failed on an arm64 virtual machines with 16k > pages. The VM has 8GB of memory. Not sure if this is the same issue that > this patch attempts to address. It is the same issue. Memory usage for the test case, assuming 64-bit page table entries: 4K pages: 512 x 2M = 1G 16K pages: 2048 x 32M = 64G 64K pages: 8192 x 512M = 4T 64G is a lot, but I don't think we want to give up on this test case on 16k machines completely. Maybe we should treat a failure to allocate a huge page here as a skip, not a fail? And remove the PMD-size gating. Zenghui, do you want to experiment with this? -- Kiryl Shutsemau / Kirill A. Shutemov