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b=kBVLE9FkkIIsMKOtrxXdEEiwCXevF/PIaAObW4zLdjVaHFPLE/BIIsvU3Hv+I/5Pg UCfvU89rsD7fvrcuAkPqbq/+o/inP9vjfg/9MK6jbBUmcCha6w0DH9xZO2l9apPzR9 FDVxl8y4Kl4nNfmdfWCkKxBT7YS0+KG92suqdm9P/8NwG78tVr7HpAzrSY1y8MPQ8S vBmYqVpcdgYMAUAWV3WNS3P4Rp22pf/lyeLPFoSlGN8wXWXivLjwtw6JW8JavmC1w+ 9ttMFU9r29etOP5oQYQ84CZLfkvpc3D9Wt9atddMTCqacDFAj8ItSJYT4yMOxz263r NfAlawwuc9L6g== Message-ID: <42b977d1-4873-4b3e-9107-7055836cde11@kernel.org> Date: Mon, 9 Feb 2026 17:03:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: clear page->private in free_pages_prepare() To: Zi Yan Cc: Vlastimil Babka , Mikhail Gavrilov , linux-mm@kvack.org, akpm@linux-foundation.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, npiggin@gmail.com, linux-kernel@vger.kernel.org, kasong@tencent.com, hughd@google.com, chrisl@kernel.org, ryncsn@gmail.com, stable@vger.kernel.org, willy@infradead.org References: <209207FE-D3A9-4BE2-8DA7-9BE38A19F387@nvidia.com> <20260207173615.146159-1-mikhail.v.gavrilov@gmail.com> <51f96b31-fb59-4cda-9d33-e3cebc45686b@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E541D140015 X-Stat-Signature: acizf3cc5cjyo7o6rqh3ofmmio1yuqxw X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1770653005-520982 X-HE-Meta: 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 5CKXktEO hSAw7oO0RdVL/EFx8LIW7oLkmoUykZORtEo2DeXQlnLhmPh7WX7THzYPEfrJCNy9PWQuomDJNcePh6KkmqtKJMKhGjWl5A0f9syCK/NzhwbQZBGQdFXApaapi9vFA/hpLKYZhMQhb4wbJPBeuOp3c/HcLJI7356jynNOWxSobpX2kLYCmaqIOPvrA4W7m6WLQSzxs7iyCSmhS2hC1lMCLZn5NwAw4HgvbsRlqsu1DN2ZiPdSaVAf3neLUNc35MrAQpdEyRlpOtdT2+eD0oIw4i6Vt1Aj5tcgbU7xvCNzDm/uzBFAJw6aIFzV9AYVAphlpOmJSMoY/kXuE9DtlV0gbcraFGiYe0lOFQRhh4A5HEsw5Yd5b0CUbluhDG35AVlUNSOS1 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 2/9/26 17:00, Zi Yan wrote: > On 9 Feb 2026, at 10:46, David Hildenbrand (Arm) wrote: > >> On 2/9/26 12:17, Vlastimil Babka wrote: >>> >>> If the rule is now that when upon freeing in free_pages_prepare() we clear >>> private in the head page and not tail pages (where we expect the owner of >>> the page to do it), maybe that check for tail pages should be done in the >>> is_check_pages_enabled() part of free_pages_prepare(). >>> >>> Or should the check be also in the split path because somebody can set a >>> tail private between allocation and split? (and not just inherit it from a >>> previous allocation that didn't clear it?). >> >> We ran into that check in the past, when folio->X overlayed page->private in a tail, and would actually have to be zeroed out. > > Currently, _mm_id (_mm_ids) overlaps with page->private. At split time, > it should be MM_ID_DUMMY (0), so page->private should be 0 all time. Yes, it's designed like that; because that check here caught it during development :) > >> >> So it should be part of this splitting code I think. > > It is still better to have the check and fix in place. Why do we want to > skip device private folio? I don't understand the question, can you elaborate? I asked Balbir why the check was dropped in the first place. -- Cheers, David