On 6/5/24 11:52 AM, Matthew Wilcox wrote: > On Tue, Jun 04, 2024 at 12:24:44PM +0800, alexs@xxxxxxxxxx wrote: >> From: "Alex Shi (tencent)" <alexs@xxxxxxxxxx> >> >> 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
