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b=IADNriuXuMloqcnP3VojVv6eQPZ5CHvGqQzSUV+rWO64RTnJGVw2B7FdiFpkgwwRn vGIFwEFMXWPfG4EwUm3YSQ1F9EwCGpvmzfqvLcCBlc8IUflqm4/Asqy8AKrOT9njPg kDSBOec2TPZ6CH4av7XEgso2iYXcPZekt9xWsYvAN3smKhB7qlvNCsSO8bcZ4PzJ5i P4eJ9qxqwLVCpiEd65ASVxjg36sb84JgGb2qVsdc4ItNRPf5wlugCPO1Pokkw5Lg1u l36EP5PCLRiC83Jn7PMmBhpahXspun1ZrPqjN7WAQYq4aF7wFLZiKFTGRW5wfJgvko xsnZqjxD0YoGg== Message-ID: <9e8b01f9-d1b0-44a7-86c9-97622b2baec1@kernel.org> Date: Tue, 6 Jan 2026 20:20:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7] page_alloc: allow migration of smaller hugepages during contig_alloc To: Zi Yan Cc: Gregory Price , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, richard.weiyang@gmail.com References: <20251221124656.2362540-1-gourry@gourry.net> <9c807ff8-b4ad-43d5-8034-ec7fcd0fe5d6@kernel.org> <36001B4C-A781-4571-AE65-4C00C9D215FC@nvidia.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: gjatwx4jmwn9irabb7kjpa8igrwk9n3q X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5E3961C0007 X-Rspam-User: X-HE-Tag: 1767727257-560288 X-HE-Meta: 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 3Q3+AGyU wwJCalnHRW+tjgTLS0NxT5VYFw+M4IdNH+Xu6SVuREJVINwbKhZAw5fV+KjriC4oxPzk86S6WJacN32M= 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 1/6/26 19:56, Zi Yan wrote: > On 6 Jan 2026, at 13:46, David Hildenbrand (Red Hat) wrote: > >>> - return false; >>> + /* >>> + * Only consider ranges containing hugepages if those pages are >>> + * smaller than the requested contiguous region. e.g.: >>> + * Move 2MB pages to free up a 1GB range. >>> + * Don't move 1GB pages to free up a 2MB range. >>> + * >>> + * This makes contiguous allocation more reliable if multiple >>> + * hugepage sizes are used without causing needless movement. >>> + */ >>> + if (PageHuge(page)) { >>> + unsigned int order; >>> + >>> + if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION)) >>> + return false; >>> + >>> + if (skip_hugetlb) { >>> + *skipped_hugetlb = true; >>> + return false; >>> + } >>> + >>> + page = compound_head(page); >>> + order = compound_order(page); >>> + if ((order >= MAX_FOLIO_ORDER) || >>> + (nr_pages <= (1 << order))) >>> + return false; >>> + >>> + /* >>> + * Reaching this point means we've encounted a huge page >>> + * smaller than nr_pages, skip all pfn's for that page. >>> + * >>> + * We can't get here from a tail-PageHuge, as it implies >>> + * we started a scan in the middle of a hugepage larger >>> + * than nr_pages - which the prior check filters for. >>> + */ >>> + i += (1 << order) - 1; >> >> Assuming page != compound_head(page), you'd be skipping too much. > > It might not happen based on my reasoning[1], but feel free to punch poles. :) :) hehe, I should just have read that comment more carefully. Anyhow, I wonder whether removing 6 lines of comments by just doing it properly might be better? head = compound_head(page); order = compound_order(head); ... i += (1 << order) - 1 - (page - head); In any case Acked-by: David Hildenbrand (Red Hat) -- Cheers David