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[80.187.83.110]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fa9bf8295sm28492525e9.3.2025.10.08.02.00.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Oct 2025 02:00:14 -0700 (PDT) Message-ID: <1c2fae79-69ad-45c2-8da7-31b3cd6dcda0@redhat.com> Date: Wed, 8 Oct 2025 11:00:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-new v2 1/1] mm/khugepaged: abort collapse scan on non-swap entries To: Lance Yang , Wei Yang Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, hughd@google.com, ioworker0@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mpenttil@redhat.com, npache@redhat.com, ryan.roberts@arm.com, ziy@nvidia.com References: <20251001032251.85888-1-lance.yang@linux.dev> <20251001085425.5iq2mgfom6sqkbbx@master> <1d09acbf-ccc9-4f06-9392-669c98e34661@linux.dev> <20251005010511.ysek2nqojebqngf3@master> <31c3f774-edb7-420a-a6a8-3e21f2abd776@linux.dev> <09eaca7b-9988-41c7-8d6e-4802055b3f1e@redhat.com> <29742109-13c2-4fa6-a3a1-d12b14641404@linux.dev> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3D2EE8000E X-Stat-Signature: 7cmnc4dq7weymfcoirsrs134z9wqxgjx X-Rspam-User: X-HE-Tag: 1759914019-405105 X-HE-Meta: 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 1BsGHNzY 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 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: > Second, as Wei pointed out[3], we may have a chance to get a non-swap > entry, since we will drop and re-acquire the mmap lock before > __collapse_huge_page_swapin(). To handle this, we also add a > non_swap_entry() check there. > > Note that we can unlock later what we really need, and not account it > towards max_swap_ptes. > > [1] > https://lore.kernel.org/linux-mm/09eaca7b-9988-41c7-8d6e-4802055b3f1e@redhat.com > [2] > https://lore.kernel.org/linux-mm/7df49fe7-c6b7-426a-8680-dcd55219c8bd@lucifer.local > [3] https://lore.kernel.org/linux-mm/20251005010511.ysek2nqojebqngf3@master > ``` > I replied to the new version. > I also think it makes sense to fold the change that adds the > non_swap_entry() check in __collapse_huge_page_swapin() into > this patch, rather than creating a new patch just for that :) > > Hmmm... one thing I'm not sure about: regarding the uffd-wp > race you mentioned, is the pte_swp_uffd_wp() check needed > after non_swap_entry()? It seems like it might not be ... > If we check non_swap_entry(), there is no need to check for other markers, agreed. -- Cheers David / dhildenb