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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a88c7e72c1sm15617141f8f.1.2025.07.02.04.04.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Jul 2025 04:04:07 -0700 (PDT) Message-ID: <819b61fb-ebb0-4ded-a104-01ab133b6a41@redhat.com> Date: Wed, 2 Jul 2025 13:04:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 19/29] mm: stop storing migration_ops in page->mapping To: Harry Yoo Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux.dev, linux-fsdevel@vger.kernel.org, Andrew Morton , Jonathan Corbet , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Jerrin Shaji George , Arnd Bergmann , Greg Kroah-Hartman , "Michael S. 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BC52C1C0005 X-Stat-Signature: nmbfjibfh6o8dcdif7kxk6bnb4jsi5mk X-HE-Tag: 1751454251-533524 X-HE-Meta: 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 U2O7UlfI Md0lYT46SCugGE1GJ5O7s9qLsjS4z17+D8D2OiVBdLNMWmtivbM+MtYj304KCrMKy4A1NTGfepIhNFzOe1nvxyW8GKkT9gJBlNP0hdf8iHMDLnKwzRm2dRfTHgmqPKVUl11KjhmH+d5CnWLxBK9HEoWGi65EsofjnHaOyVfiyN2segUrGOsWP1h/tQGTyL7qLWMcI 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 02.07.25 12:34, Harry Yoo wrote: > On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote: >> ... instead, look them up statically based on the page type. Maybe in the >> future we want a registration interface? At least for now, it can be >> easily handled using the two page types that actually support page >> migration. >> >> The remaining usage of page->mapping is to flag such pages as actually >> being movable (having movable_ops), which we will change next. >> >> Reviewed-by: Zi Yan >> Signed-off-by: David Hildenbrand >> --- > >> +static const struct movable_operations *page_movable_ops(struct page *page) >> +{ >> + VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page); >> + >> + /* >> + * If we enable page migration for a page of a certain type by marking >> + * it as movable, the page type must be sticky until the page gets freed >> + * back to the buddy. >> + */ >> +#ifdef CONFIG_BALLOON_COMPACTION >> + if (PageOffline(page)) >> + /* Only balloon compaction sets PageOffline pages movable. */ >> + return &balloon_mops; >> +#endif /* CONFIG_BALLOON_COMPACTION */ >> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) >> + if (PageZsmalloc(page)) >> + return &zsmalloc_mops; >> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */ > > What happens if: > CONFIG_ZSMALLOC=y > CONFIG_TRANSPARENT_HUGEPAGE=n > CONFIG_COMPACTION=n > CONFIG_MIGRATION=y Pages are never allocated from ZONE_MOVABLE/CMA and are not marked as having movable_ops, so we never end up in this function. See how zsmalloc.c deals with CONFIG_COMPACTION, especially how SetZsPageMovable() is a NOP without it. As a side note, both should probably be moved from COMPACTION to MIGRATION. Although probably in practice, anybody enabling CONFIG_MIGRATION likely also enables CONFIG_COMPACTION. -- Cheers, David / dhildenb