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[2003:cb:c721:b900:4f34:b2b7:739d:a650]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-429ded19670sm72644465e9.9.2024.08.16.03.03.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 16 Aug 2024 03:03:26 -0700 (PDT) Message-ID: <2d757ddb-cd20-4695-a978-ea413881d9b2@redhat.com> Date: Fri, 16 Aug 2024 12:03:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 4/7] mm: pgtable: try to reclaim empty PTE pages in zap_page_range_single() To: Qi Zheng Cc: hughd@google.com, willy@infradead.org, mgorman@suse.de, muchun.song@linux.dev, vbabka@kernel.org, akpm@linux-foundation.org, zokeefe@google.com, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <9fb3dc75cb7f023750da2b4645fd098429deaad5.1722861064.git.zhengqi.arch@bytedance.com> <2659a0bc-b5a7-43e0-b565-fcb93e4ea2b7@redhat.com> <42942b4d-153e-43e2-bfb1-43db49f87e50@bytedance.com> <860f45d7-4d75-4d67-bf2a-51f6000cd185@bytedance.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 35F2B20029 X-Stat-Signature: pb58e69pjkg3s65iuh6658ypuywtau6z X-HE-Tag: 1723802613-700332 X-HE-Meta: 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 tKj9UOTk cKSlITZwckUUWOKrLpUxXCCTbPrf6dZg85/z+OzAXM0oeMA6BvGFyAT5wLqqnDyvrzwbhsbOxXlAHI0xL/ETb7hV1b27cdq/zKSDwm9p68yt9Xb7uDbGWSltaEpoYpoIJhO2of8t6+Ae6Y7+RsrEMQNSKtv1RQUK8zQ4F42ESGJ4P7JBwTL/7CXqF93cg87CoAErrt4etRTs9BrWU4bF2q/lJdTa394Y1qL3EjKmIn9l7TIxDAkFFdO5YxTh+2tI0tmvDubB7uoShkmYJbQDuJVyBtUGk9Ualuh2pdOw+zIB0asyd1ziFbzmGrDkekBRJLT7jJl7FVsPJY+XrzLok2RysPvbFsZZ2mZ7+nCPOa9eOrniPFfB5I+eUU2TsUDEMPC90UwkBqRfFYMuYJ+8++f03va2VW9NUmvRdzO3MDHnD5qwF22kV43WEHNp5diNbIDqDREWmCzt36U7ZgS1xVetxWg== 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: >> >> (b) if we didn't have to drop the PTL, we can remove the page table >>     without even re-verifying whether the entries are pte_none(). We > > If we want to remove the PTE page, we must hold the pmd lock (for > clearing pmd entry). To prevent ABBA deadlock, we must first release the > pte lock and then re-acquire the pmd lock + pte lock. Right? If so, then > rechecking pte_none() is unavoidable. Unless we hold the pmd lock + pte > lock in advance to execute the original code loop. Try-locking the PMD should work, and succeed in many cases, right? And if that fails, we could fallback to what you describe. -- Cheers, David / dhildenb