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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tVCYW-00000008FlJ-2TSc; Tue, 07 Jan 2025 16:35:48 +0000 Date: Tue, 7 Jan 2025 16:35:48 +0000 From: Matthew Wilcox To: David Hildenbrand Cc: Yu Zhao , Andrew Morton , Mateusz Guzik , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Will Deacon Subject: Re: [PATCH mm-unstable v1] mm/hugetlb_vmemmap: fix memory loads ordering Message-ID: References: <20250107043505.351925-1-yuzhao@google.com> <85ea0bc9-0892-489d-b42b-430ff8a1f368@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <85ea0bc9-0892-489d-b42b-430ff8a1f368@redhat.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 3F23440023 X-Stat-Signature: 7apexwc3et1jzc693319z3tn1awmn4rt X-Rspam-User: X-HE-Tag: 1736267752-972128 X-HE-Meta: U2FsdGVkX18BLWGGsfSsNrzmQRa+PxC+C7VHbdQwwUt4UFqDWd3UJMaqZa/vgFaooJd4S0mb670fts5JH7XZyw9hi+2irtZqcmIvx8hMOGXnFfwRJyA2Ebf7uiTz7vpsd3CyZYhV413qvRKHT8JvF4KYMOugzI3d6WwERpGP6ISDnFSnpSJxrxcTg59EDjao1J1nBDhX/XgBUWvadGt5rJXYaom+Fr8t2+3sOQ7W1hxqy1G1me5LcHiTeyD8B5Bbyjb0Daq0zT+e8wQTyyBiIcsxIyLwTam1cCjIP3s1u4kkA+3aRHJUZYMQMJi9qbpwPhE+wBxo4C2YS+7NYA+9SL398VruG63DL8jzxDRIYE41ZL9/EBg+hQ9kKGD50NRHHu6HLw0NCUNqK4Lz7M7Kddyon1N2+X8u6vthml/ba0yKBrOz8iJobr4h8fbuXuZ3Vg809qo/Mp6+0HPcNE8OrPbcloxpKSVN5DlmAVR9Mw41CGaA2kOGEWEAHzFnHmGku+XELUEEHHsJHn7wim5J0B6JrZ8OW8icZkyrPQT77g+w57F6TkWGfKQKCBJYvvNczpmdGknShSY6fkJddAMcXiA+bJ134FJhbKKTS0RwvmV5brNTQJuT2Q9SAqVvGS8YawalqZ+SatOrR8Pr3ZaF/WlsNBNk16dkdeTmo2MLVQtCJuFhOxewLSlhE5BC0QD8saVYjgnveQEqVN+DIk2b88Jln9tXsSytOQtLFbU1lUBjBq0XosA+zBKxUTwcEiOwkzEHngCy+SV3QvBts3Q/XtCNDmC+zRCWM+Zkw2c8EDIuQCxytkRVqxSMOoExirJanUt9d1hOaIi2eeRjNpTS+CwD49dDjKlp5tCzDPpOiquNW1fQyrVv4K7SVWPv1IPSPEUnznzVwnDdJT/hmmaXhKzeYWagPM4OclYiy7LvC/Bfw2F+mlpefk+dm6Btwd1HIxq15aWPp8JT+OJAh8y MNM5miYJ F3otnMUtwcZfqo76p3pF4uizisl+6MFpN2v8l36i5HmP7XvEZYHmqLcvxKPuE1Ity9QNjZ2IYXxnwVp9SntRt9rzXFPiuLqf2ea5j9DynFA3qUw7SjMsx5SOjuuKQkv1XC82QYUpMCCl2N3snnUmvRerYg/YjGJIfavcANKnICNXBoJsd2soyLUuNDG2dePQTr68MpbOdI4FUgL84tAXq2c14UaG9x1s7Z5m7TlQNS7CYIhs5l6VCz8srThFafyy5+dy+LTlTTbfJLk/BlSNz8DwntQ== 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 Tue, Jan 07, 2025 at 09:49:18AM +0100, David Hildenbrand wrote: > > +++ b/include/linux/page-flags.h > > @@ -212,7 +212,7 @@ static __always_inline const struct page *page_fixed_fake_head(const struct page > > * cold cacheline in some cases. > > */ > > if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) && > > - test_bit(PG_head, &page->flags)) { > > + test_bit_acquire(PG_head, &page->flags)) { > > This change will affect all page_fixed_fake_head() users, like ordinary > PageTail even on !hugetlb. I've been looking at the callers of PageTail() because it's going to be a bit of a weird thing to be checking in the separate-page-and-folio world. Obviously we can implement it, but there's a bit of a "But why would you want to ask that question" question. Most current occurrences of PageTail() are in assertions of one form or another. Fair enough, not performance critical. make_device_exclusive_range() is a little weird; looks like it's trying to make sure that each folio is only made exclusive once, and ignore any partial folios which overlap the start of the area. damon_get_folio() wants to fail for tail pages. Fair enough. split_huge_pages_all() is debug code. page_idle_get_folio() is like damon. That's it. We don't seem to have any PageTail() callers in critical code any more.