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Thu, 10 Sep 2026 06:59:30 -0400 (EDT) Date: Thu, 10 Sep 2026 11:59:29 +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 06/19] selftests/mm: stop khugepaged during the MADV_COLLAPSE cases Message-ID: References: <20260908125105.1510704-1-kirill@shutemov.name> <20260908125105.1510704-7-kirill@shutemov.name> <4e064b9d-aea9-485a-8547-3830999cff01@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: e6dgiudi3jd4m634rcr5i35m1y83tpzs X-Rspam-User: X-Rspamd-Queue-Id: 89E8A20009 X-Rspamd-Server: rspam03 X-HE-Tag: 1789037971-692158 X-HE-Meta: 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 hG5drZJr 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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 Thu, Sep 10, 2026 at 02:27:28PM +0800, Baolin Wang wrote: > > > On 9/9/26 6:41 PM, Kiryl Shutsemau wrote: > > On Wed, Sep 09, 2026 at 05:55:01PM +0800, Baolin Wang wrote: > > > > > > > > > On 9/8/26 8:50 PM, Kiryl Shutsemau wrote: > > > > From: "Kiryl Shutsemau (Meta)" > > > > > > > > __madvise_collapse() turns THP off before each MADV_COLLAPSE, both to keep > > > > khugepaged out of the range and to prove MADV_COLLAPSE ignores the setting. > > > > It clears the global controls only, which is no longer enough. A per-order > > > > control overrides them, and -s, which makes the cases fault in folios of > > > > one order, leaves that order's control at "always". khugepaged then > > > > collapses the very range the case is working on, and the case fails on a > > > > collapse that was interfered with rather than refused. > > > > > > Right. So I think the correct fix tag is b7f16963efe7 ("mm/khugepaged: run > > > khugepaged for all orders"), because before this commit, khugepaged would > > > not try to collapse this range since it only checked whether the PMD order > > > was suitable for collapse. > > > > Agreed. The series is in mm-new already; if a respin is needed I will use > > that tag. > > > > > > @@ -547,9 +547,16 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages, > > > > /* > > > > * Prevent khugepaged interference and tests that MADV_COLLAPSE > > > > * ignores /sys/kernel/mm/transparent_hugepage/enabled > > > > + * > > > > + * "inherit" rather than "never" so that MADV_COLLAPSE on shmem still > > > > + * finds an order to build. > > > > */ > > > > settings.thp_enabled = THP_NEVER; > > > > settings.shmem_enabled = SHMEM_NEVER; > > > > + for (i = 0; i < NR_ORDERS; i++) { > > > > + settings.hugepages[i].enabled = THP_INHERIT; > > > > + settings.shmem_hugepages[i].enabled = SHMEM_INHERIT; > > > > + } > > > > > > This looks like a workaround to me. Shouldn't we fix this in shmem instead? > > > > Good point. > > > > It can be a follow-up patch. Do you want to make a proper shmem.c fix > > and update the selftest along with it? > > Either way works for me. Please, do it as a standlone shmem fix, plus selftest update to reflect the change. -- Kiryl Shutsemau / Kirill A. Shutemov