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Tue, 16 Sep 2025 05:48:24 -0400 (EDT) Date: Tue, 16 Sep 2025 10:48:22 +0100 From: Kiryl Shutsemau To: Lorenzo Stoakes Cc: Lance Yang , Hugh Dickins , akpm@linux-foundation.org, david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH mm-new 1/3] mm/khugepaged: skip unsuitable VMAs earlier in khugepaged_scan_mm_slot() Message-ID: <3az7vzkhpa2pup3td5pbrek6ti2fij574qimtnbpecums7ixyl@upabkyqmtiaf> References: <20250914143547.27687-1-lance.yang@linux.dev> <20250914143547.27687-2-lance.yang@linux.dev> <2466c068-ccd7-41a1-bef7-6f3fefc6ff55@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2466c068-ccd7-41a1-bef7-6f3fefc6ff55@lucifer.local> X-Rspamd-Queue-Id: 1BF0A40012 X-Stat-Signature: xbrwxtuydroukqq8hx74utpauytnceyk X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1758016106-191373 X-HE-Meta: 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 DaYDlnGP hUNTE+km/EmDVSaveJOJqmaRPPUShu27llgNI7HVvWw8elLKSmKBy3Ntc4XvXlxSDJDlEH2eNBYEpFHHocB4LB6RGZAvhhazqmtmnsJbM/pGUx1Li5UnkNdhytveKEspkk0VlcAGMf3qGEgUXOcmxcntJG8KqnztzWoCqVkuUZF4pINjYQIaNjoLnbtqIfdKnpzklG+uNMw1nqs2lFdfPrOMvLyHGKvhLq5fa2jWIfwxTRusAdHxSf3TTLEQiIe3Ak9XzyXx21jgwE1Tqcd6N4Zsjc5GetVBNbahP6KOSPrgC2XcHNfaKc1SbeVW3Ydq4ozzEExTbAkU+BDQm8lZcM1ntB5N0mIx3b6h76SfO4Rt/TnhbzPYgltMvATX/3bZ9qQf/SuNAD5AyNWpPzF/CiWI3390iMP8TaA63MVEdTLmxTieudf619MDtueOwb/bFmFWeKq6Mk1VADUqcHEcY/7mtVA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 16, 2025 at 10:39:53AM +0100, Lorenzo Stoakes wrote: > On Tue, Sep 16, 2025 at 10:29:11AM +0100, Kiryl Shutsemau wrote: > > On Tue, Sep 16, 2025 at 02:21:26PM +0800, Lance Yang wrote: > > > Users of mlock() expect low and predictable latency. THP collapse is a > > > heavy operation that introduces exactly the kind of unpredictable delays > > > they want to avoid. It has to unmap PTEs, copy data from the small folios > > > to a new THP, and then remap the THP back to the PMD ;) > > > > Generally, we allow minor page faults into mlocked VMAs and avoid major. > > This is minor page fault territory in my view. > > Hm, but we won't be causing minor faults via reclaim right, since they're > not on any LRU? PTEs are still present when we do THP allocation. No reclaim while the access is blocked. We only block the access on copy and PTEs->PMD collapse. -- Kiryl Shutsemau / Kirill A. Shutemov