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Tue, 18 Aug 2026 10:58:04 +0000 X-Migadu-Flow: FLOW_OUT Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 18 Aug 2026 12:58:03 +0200 Message-Id: Cc: "Vlastimil Babka (SUSE)" , "Borislav Petkov" , "Dave Hansen" , "Peter Zijlstra" , "Andrew Morton" , "David Hildenbrand" , "Mike Rapoport" , "Wei Xu" , "Johannes Weiner" , "Zi Yan" , "Lorenzo Stoakes" , , , , "Sumit Garg" , "Will Deacon" , , , "Itazuri, Takahiro" , "Andy Lutomirski" , "David Kaplan" , "Thomas Gleixner" , "Patrick Bellasi" , "Reiji Watanabe" , "Sean Christopherson" Subject: Re: [PATCH v3 19/26] mm/page_alloc: rename ALLOC_NON_BLOCK back to _HARDER From: "Brendan Jackman" To: "Yosry Ahmed" , "Brendan Jackman" X-Mailer: aerc 0.21.0 References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-19-6f5729aa9832@google.com> In-Reply-To: X-Stat-Signature: py6jgy6ua6mo1m8ynozakojdt99x53df X-Rspamd-Queue-Id: 74963100009 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1787050686-101227 X-HE-Meta: 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 MG+WA/uv iUIiznMcR70JPEOFWUvZkt2ql9c2CCId6r0qIaRXmL9z15MjOgqLGp0HT7n1eQLoeBrD8WhDu4onjmt1cxiTHItf4/H4XrqzNRvAULfnuZuqhCn8onJVK0/fXBptS26wK6UgFM0k8sXlwF4BKY634awYGze0PeCQmqKTci3q5p/7sjl0M7a/wX1SiEAPCajwSiiA8vJ5wGjXi2QerpebnQ9sausMp0HtjM+qDarTfulLV+Meoc/6MfcHBoJSFZvPwlOkY5XeCnPguF6kLA9sU7HKcAf2e6CKlFoJ1zTJEDPuDR+DabVgf4wjMX19R/yhDMlG/Vw7VRQbYwGAt71IdHPBKYBXZdcHwIrAn1dEZAw1MK1Nf/daFTRLQwouBgeyREjtN Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue Aug 18, 2026 at 2:45 AM CEST, Yosry Ahmed wrote: > On Fri, Aug 14, 2026 at 01:09:32PM +0100, Brendan Jackman wrote: >> On Tue Aug 4, 2026 at 10:50 PM BST, Yosry Ahmed wrote: >> > On Fri, Jul 31, 2026 at 04:52:59PM +0200, Vlastimil Babka (SUSE) wrote= : >> >> On 7/27/26 00:22, Brendan Jackman wrote: >> >> > Commit 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HI= GH >> >> > non-blocking allocations accesses reserves") renamed ALLOC_HARDER t= o >> >> > ALLOC_NON_BLOCK because the former is "a vague description". >> >> >=20 >> >> > However, vagueness is accurate here, this is a vague flag. It is no= t set >> >> > for __GFP_NOMEMALLOC. It doesn't really mean "allocate without bloc= king" >> >> > but rather "allow dipping into atomic reserves, _because_ of the ne= ed >> >> > not to block". >> >> >=20 >> >> > A later commit will need an alloc flag that really means "don't blo= ck >> >> > here", so go back to the flag's old name and update the commentary >> >> > to try and give it a slightly clearer meaning. >> >> >=20 >> >> > Signed-off-by: Brendan Jackman >>=20 >> Writing this to get it clear in my head, so I'll also dump it in the >> mail in case it helps get us on the same page...=20 >>=20 >> What we actually want here is a flag that tells us when we can do a TLB >> shootdown. That means (on x86) that IRQs must be on and we mustn't be >> holding some random spinlock (most spinlocks would actually be fine but >> I think it's simpler to assume we can't hold any).=20 >>=20 >> It must never be over-permissive i.e. tell us we can do a TLB flush >> when we can't. It's fine to _sometimes_ be over-restrictive i.e. tell us >> we can't do a TLB flush when we can, but if it always forbids flushing >> while GFP_BOOT_MASK is in effect then we'll fail critical allocations >> and crash. > > Why is it a problem if it forbids flushing while GFP_BOOT_MASK is in > effect? We should change gfp_allowed_mask before any unmapped > allocations are possible, right? Hm, good point... I don't remember why this was a problem. It certainly seems like it shoudl be OK for secretmem and guest_memfd.