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Tue, 12 May 2026 20:10:27 -0700 (PDT) Message-ID: <85de3792-596b-4efb-b2a9-89556e098f01@gmail.com> Date: Wed, 13 May 2026 11:10:19 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/memory: avoid unnecessary #PF on mTHP allocation race To: "David Hildenbrand (Arm)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com References: <20260512095031.1333997-1-chenwandun@lixiang.com> <220524ba-e39a-4d7f-b44f-d4e2e7132397@kernel.org> Content-Language: en-US From: Wandun In-Reply-To: <220524ba-e39a-4d7f-b44f-d4e2e7132397@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/12/26 18:35, David Hildenbrand (Arm) wrote: > On 5/12/26 11:50, Wandun Chen wrote: >> When an mTHP folio is allocated in do_anonymous_page() and the target >> pte range is not fully empty, current code would release the folio >> and return. >> >> This results an illusion that a page fault has already been processed >> even if the fact is vmf->address itself is still pte_none(). Another >> page fault will be triggered again. > Yes. Why is that a problem? Honestly, the only data I have is the reproducer; I haven't been able to show a measurable impact on a real workload. The motivation was "we did the work of allocatingan mTHP folio and then throw it away just to redo it from #PF, and this #PF can be avoided by adding a small check + retry". But as you point out, the second fault path can handle this case properly, the behaviour is already correct.Please drop the patch. I'll come back with numbers if I run into a workload where this race is actually hot.Thanks for taking a look. Best regards, Wandun >