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Thu, 04 Sep 2025 20:11:30 -0700 (PDT) Date: Fri, 5 Sep 2025 03:11:30 +0000 From: Wei Yang To: Zi Yan Cc: Wei Yang , akpm@linux-foundation.org, linux-mm@kvack.org, Johannes Weiner , David Hildenbrand , Baolin Wang , Vlastimil Babka Subject: Re: [PATCH] mm/page_alloc: check the correct buddy if it is a starting block Message-ID: <20250905031129.lgipzjwz2swhxlg7@master> Reply-To: Wei Yang References: <20250904020654.28689-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B6B2C40008 X-Stat-Signature: s1z1oqakgyd17xdxqf3r9j156oopkufk X-Rspam-User: X-HE-Tag: 1757041892-665413 X-HE-Meta: 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 6MqYEmtS 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 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 Thu, Sep 04, 2025 at 10:01:01PM -0400, Zi Yan wrote: >On 3 Sep 2025, at 22:06, Wei Yang wrote: > >> find_large_buddy() search buddy based on start_pfn, which maybe >> different from page's pfn, e.g. when page is not pageblock aligned, >> because prep_move_freepages_block() always align start_pfn to pageblock. >> >> This means when we found a starting block at start_pfn, it may check >> on the wrong page theoretically. > >and not split the free page as it is supposed to, causing a freelist migratetype >mismatch. > Thanks, this is important. >> >> The good news is the page passed to __move_freepages_block_isolate() has >> only two possible cases: >> >> * page is pageblock aligned >> * page is __first_valid_page() of this block >> >> So it is safe for the first case, and it won't get a buddy larger than >> pageblock for the second case. >> >> To eliminate the ambiguity, unify the handling for starting/tail block. > >To fix the issue, check the returned pfn of find_large_buddy() to decide >whether to split the free page: >1. if it is not a PageBuddy pfn, no split; >2. if it is a PageBuddy pfn but order <= pageblock_order, no split; >3. if it is a PageBuddy pfn with order > pageblock_order, > start_pfn is either in the starting block or tail block, split the PageBuddy > at pageblock_order level. > > >Otherwise, LGTM. Reviewed-by: Zi Yan Thanks. @Andrew, if not bother, would you mind adjust the changelog? -- Wei Yang Help you, Help me