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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: mkqewciqygtdks9qnpzascgeqakmnxzn X-Rspamd-Queue-Id: 8EF821C001A X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1717568058-547081 X-HE-Meta: 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 slacJMtn 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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 6/5/24 11:52 AM, Matthew Wilcox wrote: > On Tue, Jun 04, 2024 at 12:24:44PM +0800, alexs@kernel.org wrote: >> From: "Alex Shi (tencent)" >> >> When a folio isn't fit for KSM, the subpages are unlikely to be good, >> So let's skip the rest page checking to save some actions. > > Why would you say that is true? We have plenty of evidence that > userspace allocators can allocate large folios, then use only the first > few bytes, leaving many tail pages full of zeroes. Um, that do need tail pages... Is there some way to use more folio in ksm? > >> @@ -2660,6 +2662,9 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) >> cond_resched(); >> continue; >> } >> + >> + VM_WARN_ON(PageTail(*page)); >> + nr = compound_nr(*page); > > And this is simply wrong. *page can obviously be a tail page. > Got it. Thanks a lot! Alex