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b=F2Wi+SzmE8NANJECWnAds8jawhETcoSZ6qmBMOfNAbYqiP+9K94ldEI85PmV0MX1b Wl/7HnW0dyheM+JnE6KXmb6vl+J9tT6H8FaEuXlNw519ilYLMay1bJNxnghjfhNvdn GmOksC+r+1NiQrDWfNnWSrky+n4RLaeObHRY5jRo= Date: Wed, 2 Apr 2025 20:49:31 -0700 From: Andrew Morton To: Jinjiang Tu Cc: , , , , Subject: Re: [PATCH v2] mm/hugetlb: fix set_max_huge_pages() when there are surplus pages Message-Id: <20250402204931.78a02332bcd9d9e9db970fd0@linux-foundation.org> In-Reply-To: <20250401082339.676723-1-tujinjiang@huawei.com> References: <20250401082339.676723-1-tujinjiang@huawei.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: EF15B40007 X-Stat-Signature: cqwg1k6w64ezsjn94gtfq9sbqugmg3mj X-Rspam-User: X-HE-Tag: 1743652173-166371 X-HE-Meta: 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 Ffl/Qjta D6Hncfob2EEZ2PzxjW3aHYPaNcN/2ehxCOHvM2WDbWRm8XErhQ0XcWHqNYfh9vUzFvfEp9iRtyf/VT1WleJo9wSTAq9vtNPQ+6+Xb59T/b6yPozTA/duLLF7RPKsF2k7Udc9PD8gWjH0hNesvJxY7PGNwbQsky2dThoVojZcqHoHbCo6+fWhSg2+ZcEH3inuRatGnr9Ar5CCdPUT9Re9eXjiCx2op/MPMB1Y5QkYznUuT2WQNvH7woVIoFU7M+0BrnCV/NabrDTcqvSM5iH5TU/Stq0daB/tgwhZdaZrmr22kq99GGTm/UwoFh+KvYXWxfwJo 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 Tue, 1 Apr 2025 16:23:39 +0800 Jinjiang Tu wrote: > In set_max_huge_pages(), min_count should mean the acquired persistent > huge pages, but it contains surplus huge pages. It will leads to failing > to freeing free huge pages for a Node. > > Steps to reproduce: > 1) create 5 hugetlb folios in Node0 > 2) run a program to use all the hugetlb folios > 3) echo 0 > nr_hugepages for Node0 to free the hugetlb folios. Thus the 5 > hugetlb folios in Node0 are accounted as surplus. > 4) create 5 hugetlb folios in Node1 > 5) echo 0 > nr_hugepages for Node1 to free the hugetlb folios > > The result: > Node0 Node1 > Total 5 5 > Free 0 5 > Surp 5 5 > > We couldn't subtract surplus_huge_pages from min_mount, since free hugetlb > folios may be surplus due to HVO. In __update_and_free_hugetlb_folio(), > hugetlb_vmemmap_restore_folio() may fail, add the folio back to pool and > treat it as surplus. If we directly subtract surplus_huge_pages from > min_mount, some free folios will be subtracted twice. > > To fix it, check if count is less than the num of free huge pages that > could be destroyed (i.e., available_huge_pages(h)), and remove hugetlb > folios if so. > > Since there may exist free surplus hugetlb folios, we should remove > surplus folios first to make surplus count correct. > > The result with this patch: > Node0 Node1 > Total 5 0 > Free 0 0 > Surp 5 0 Thanks. > Fixes: 9a30523066cd ("hugetlb: add per node hstate attributes") 16 years ago. How do people feel about a -stable backport?