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To: Vlastimil Babka , Qiang Liu , Kemeng Shi Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20241114065720.3665-1-liuq131@chinatelecom.cn> <2b6ca5b1-f421-4dda-a2a2-865af97b2db8@suse.cz> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Stat-Signature: mwgyxuxschfj1spqskjptggnmbdfxcrb X-Rspamd-Queue-Id: B808C407CD X-Rspam-User: X-HE-Tag: 1731578724-806589 X-HE-Meta: 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 rJjg02eu tvyDX0x3Kay08Je9T1oJjwO3zGicOkGADYqkW2SWrBlgbqq/tk53lUx2dA6rbv7uuacZVSLaPIeQgCOMjDkdzkJ0HpQhR7E7nGmM/YmTHALdj9PG26jQF6FKk9v6l9iF4S1kCt4UoEY0pUJsU9GRKMbx+5Shx8xH0p6iUUh6oVVWB9H8r5Hd1sbiY/eI6cHqIgd+WvqYmpdBt5WLQxC/M2mN04sORvPlGhxTGSdxAEnXr4l2RobJDcOpYNg== 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 2024/11/14 15:52, Vlastimil Babka wrote: > On 11/14/24 08:44, Vlastimil Babka wrote: >> On 11/14/24 07:57, Qiang Liu wrote: >>> It is impossible for the situation where blockpfn > end_pfn to arise, >>> The if statement here is not only unnecessary, but may also lead to >>> a misunderstanding that blockpfn > end_pfn could potentially happen. >>> so these unnecessary checking code should be removed. >>> >>> Signed-off-by: Qiang Liu >> >> I see that's since 3da0272a4c7d ("mm/compaction: correctly return failure >> with bogus compound_order in strict mode") > > Hm but we still have: > > for (; blockpfn < end_pfn; blockpfn += stride, page += stride) { > > and this advance by stride can mix up with advance by isolated, initial pfn > might not be aligned... I don't see any guarantee that the for loop will > exit with exactly blockpfn == end_pfn, it may easily advance beyond end_pfn > so we shouldn't remove the check? Agreed. >> I think that commit introduced a risk of overflow due to a bogus order >> (which we read in a racy way), and once blockpfn overflows it will satisfy >> <= end_pfn and might e.g. end up scanning a completely different zone? >> >> if (blockpfn + (1UL << order) <= end_pfn) { >> >> blockpfn += (1UL << order) - 1; >> page += (1UL << order) - 1; >> nr_scanned += (1UL << order) - 1; >> } >> >> We should better add back the MAX_ORDER sanity check? >> >>> --- >>> mm/compaction.c | 6 ------ >>> 1 file changed, 6 deletions(-) >>> >>> diff --git a/mm/compaction.c b/mm/compaction.c >>> index a2b16b08cbbf..baeda7132252 100644 >>> --- a/mm/compaction.c >>> +++ b/mm/compaction.c >>> @@ -682,12 +682,6 @@ static unsigned long isolate_freepages_block(struct compact_control *cc, >>> if (locked) >>> spin_unlock_irqrestore(&cc->zone->lock, flags); >>> >>> - /* >>> - * Be careful to not go outside of the pageblock. >>> - */ >>> - if (unlikely(blockpfn > end_pfn)) >>> - blockpfn = end_pfn; >>> - >>> trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn, >>> nr_scanned, total_isolated); >>> >> >>