On Tue, Jan 04, 2022 at 11:36:29PM -0800, John Hubbard wrote: > > - SetPageReferenced(page); > > + folio_set_referenced(folio); > > For the case of a tail page, I *think* the above hunk changes the > behavior. Previously, the tail page's flags were affected, but now, the > head page's (folio's) page flags are being changed...right? So ... most flags don't really "exist" for tail pages. PAGEFLAG(Referenced, referenced, PF_HEAD) #define PF_HEAD(page, enforce) PF_POISONED_CHECK(compound_head(page)) so any time you call SetPageReferenced(page), we have a hidden call to compound_head() in order to set PG_referenced on the head page. It's only the PF_ANY flags which are (theoretically) settable on tail pages: PAGEFLAG(Private, private, PF_ANY) PAGEFLAG(Private2, private_2, PF_ANY) PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY) PAGEFLAG(HWPoison, hwpoison, PF_ANY) TESTPAGEFLAG(Young, young, PF_ANY) PAGEFLAG(Idle, idle, PF_ANY) __PAGEFLAG(Head, head, PF_ANY) __PAGEFLAG(Isolated, isolated, PF_ANY) I honestly doubt many of these are actually settable on tail pages; it's simply that nobody's really thought about them for compound pages.
