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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=C4E+9Sxx; dmarc=pass (policy=reject) header.from=nvidia.com; spf=none (imf12.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.93.48) smtp.mailfrom=jhubbard@nvidia.com X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D3B394000C X-Stat-Signature: hjdhms551zimrocj6igpeo6uf9czoqg7 X-HE-Tag: 1641369398-27309 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: On 1/4/22 23:52, Matthew Wilcox wrote: > 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. OK, I see. Thanks for spelling that out for me. :) Please feel free to add: Reviewed-by: John Hubbard thanks, -- John Hubbard NVIDIA