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rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH] mm/page_alloc: consider pfn holes after pfn_valid() in __pageblock_pfn_to_page() To: Michal Hocko Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <62e231a8f2e50c04dcadc7a0cfaa6dea5ce1ec05.1681296022.git.baolin.wang@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: mnxro5cfykfdgxnx3ue1dqaex6xqidrt X-Rspam-User: X-Rspamd-Queue-Id: E0943C0005 X-Rspamd-Server: rspam06 X-HE-Tag: 1681302249-331606 X-HE-Meta: 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 1u75Soj3 C6K7xaTiJy8oYuYMXv6M2ndWlrWRXS6XyEyzwpcRLuvbYYsPR5S913QhB5r7/PQOtdB9/xehw4EhxWxyPELgpHoMtR5Vc7kSCLQKNnRH5zTbV3vH/MrnhRFcZMexEKjHO5tnhkhSlW90P0dajm2asNVrT2g== 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: On 4/12/2023 7:15 PM, Michal Hocko wrote: > On Wed 12-04-23 18:45:31, Baolin Wang wrote: >> Now the __pageblock_pfn_to_page() is used by set_zone_contiguous(), >> which checks whether the given zone contains holes, and uses pfn_valid() >> to check if the end pfn is valid. However pfn_valid() can not make sure >> the end pfn is not a hole if the size of a pageblock is larger than the >> size of a sub-mem_section, since the struct page getting by pfn_to_page() >> may represent a hole or an unusable page frame, which may cause incorrect >> zone contiguous is set. >> >> Though another user of pageblock_pfn_to_page() in compaction seems work >> well now, it is better to avoid scanning or touching these offline pfns. >> So like commit 2d070eab2e82 ("mm: consider zone which is not fully >> populated to have holes"), we should also use pfn_to_online_page() for >> the end pfn to make sure it is a valid pfn with usable page frame. >> Meanwhile the pfn_valid() for end pfn can be dropped now. >> >> Moreover we've already used pfn_to_online_page() for start pfn to make >> sure it is online and valid, so the pfn_valid() for the start pfn is >> unnecessary, drop it. > > Is this a theoretical problem or something you have encountered on a > real machine? Could you provide more details please? As I replied to David, this is just from code inspection when trying to remove the unnecessary pfn_valid() in __pageblock_pfn_to_page().