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Wed, 27 Mar 2024 08:06:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id nGAbBYrTA2aJBAAAD6G6ig (envelope-from ); Wed, 27 Mar 2024 08:06:34 +0000 Message-ID: Date: Wed, 27 Mar 2024 09:06:33 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 09/10] mm: page_isolation: prepare for hygienic freelists To: Johannes Weiner , Andrew Morton Cc: Mel Gorman , Zi Yan , "Huang, Ying" , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240320180429.678181-1-hannes@cmpxchg.org> <20240320180429.678181-10-hannes@cmpxchg.org> Content-Language: en-US From: Vlastimil Babka In-Reply-To: <20240320180429.678181-10-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 4mxaqpujfyrt55zekom547h8s5t1dysr X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6C367A0004 X-Rspam-User: X-HE-Tag: 1711526796-490415 X-HE-Meta: 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 wEpCIbnb u8lKmf3Jk4fHjwtw= 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 3/20/24 7:02 PM, Johannes Weiner wrote: > Page isolation currently sets MIGRATE_ISOLATE on a block, then drops > zone->lock and scans the block for straddling buddies to split > up. Because this happens non-atomically wrt the page allocator, it's > possible for allocations to get a buddy whose first block is a regular > pcp migratetype but whose tail is isolated. This means that in certain > cases memory can still be allocated after isolation. It will also > trigger the freelist type hygiene warnings in subsequent patches. > > start_isolate_page_range() > isolate_single_pageblock() > set_migratetype_isolate(tail) > lock zone->lock > move_freepages_block(tail) // nop > set_pageblock_migratetype(tail) > unlock zone->lock > __rmqueue_smallest() > del_page_from_freelist(head) > expand(head, head_mt) > WARN(head_mt != tail_mt) > start_pfn = ALIGN_DOWN(MAX_ORDER_NR_PAGES) > for (pfn = start_pfn, pfn < end_pfn) > if (PageBuddy()) > split_free_page(head) > > Introduce a variant of move_freepages_block() provided by the > allocator specifically for page isolation; it moves free pages, > converts the block, and handles the splitting of straddling buddies > while holding zone->lock. > > The allocator knows that pageblocks and buddies are always naturally > aligned, which means that buddies can only straddle blocks if they're > actually >pageblock_order. This means the search-and-split part can be > simplified compared to what page isolation used to do. > > Also tighten up the page isolation code around the expectations of > which pages can be large, and how they are freed. > > Based on extensive discussions with and invaluable input from Zi Yan. > > Signed-off-by: Johannes Weiner Nice cleanup of hairy code as well! Reviewed-by: Vlastimil Babka