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[109.81.95.234]) by smtp.gmail.com with UTF8SMTPSA id 4fb4d7f45d1cf-639cd144d13sm2491125a12.19.2025.10.08.00.52.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Oct 2025 00:52:52 -0700 (PDT) Date: Wed, 8 Oct 2025 09:52:51 +0200 From: Michal Hocko To: Wei Yang Cc: Andrew Morton , vbabka@suse.cz, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, iamjoonsoo.kim@lge.com, linux-mm@kvack.org Subject: Re: [PATCH 0/2] mm/compaction: some fix for the range passed to pageblock_pfn_to_page() Message-ID: References: <20251002033140.24462-1-richard.weiyang@gmail.com> <20251007182922.4a254daff78633b1452bdcc3@linux-foundation.org> <20251008023218.g53gm33vmrdt5nw7@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251008023218.g53gm33vmrdt5nw7@master> X-Stat-Signature: 8tsm48ft6xz8yjrnnrescd6qwrerigqx X-Rspamd-Queue-Id: 751B640009 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1759909974-691159 X-HE-Meta: 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 Ul5TLQpW 9K+aEHt0C+eeU9TtrnjksjmzVVuuytETaap44IMuBaGdRyCFWj2uCwRzLYZyRAIUqByRqxy7P+83B1uzlztjrCHqjO3EXkoCBFhYyaZ15dgLjOSUZlKeVN4gbJJWoXtAkyOvhVvcia0YQ/O13yS4+DBeq7rqNV94XBmDpdEsA3K4vjZEXpHZJ7Z/pCOkt6G2eYtA3SqX6Nt3dhDZNkyYX5g2ehflCDeJC3DPj1TWiL0O87AIVplQe/QDYNoiSUK6AvgeeyN2JazaQNal3+KlQUuoTS85eEKSBOI1YxQgadWgXFptsjtcGbvwSQGeLn6wtAHNTyFEnlZIv2ATBIv7z+rUTnOhrTqeDvRtrMBbn7AfeGi1TMbKqC3CENks9f+cw9/2hgeK42fpo9kLlzM42p88yuLC4jRtPnFxSK0V7UfKOdhXdDZgKQJVy6EisI1ecfQwnvzX3do7dgFUx8vIbWqlooji1wY1UskcizqBtf7tBw+M= 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 Wed 08-10-25 02:32:18, Wei Yang wrote: > On Tue, Oct 07, 2025 at 06:29:22PM -0700, Andrew Morton wrote: > >On Thu, 2 Oct 2025 03:31:38 +0000 Wei Yang wrote: > > > >> During the code reading of isolate_migratepages_range(), first spot the range > >> passed to pageblock_pfn_to_page() is different from that to > >> isolate_migratepages_block(). > >> > >> This implies there is a chance that pageblock_pfn_to_page() thinks the range > >> is in the same zone, but isolate_migratepages_block() will isolate range in > >> two different zones. This is not what we expect. > >> > >> Then I found pageblock_pfn_to_page() has an optimization if zone->contiguous, > >> this means even the range is across two different zones, it will think the > >> range is within the same zone. > >> > >> So introduce two patches to fix it: > > > >What do you think might be the worst-case userspace-visible effects > >of the bug? > > I don't see userspace-visible effect yet. > > Since I lack the knowledge of the consequence of isolating cross zone range, > currently I can't tell the effect accurately. > > The worst case in my mind is we put some page on a different zone's freelist. > But I don't totally understand the behavior now. Is there any actual problem to fix here then? -- Michal Hocko SUSE Labs