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b=V5dCshPaL54uf39QVRVNzhtRdjaL3A5+N0uTPkmYLKvUY7qjSBfOWdQCCOlsY1rCr 7bbJME5plInKvwecbvPBYNAUkMlxC374eKYuWbOIP+PTlS2JcNh0su3uUY1KsBAKzH zj8GY3MUqT2Wc8mimnl+E8J1hEfnqrTUCeyxA1Jlnr6xQTA0MLwKnnO5BKagPO+dTp v/+zldvzIj8sXoT4EMZDcD03UeU+WJ2Xu6TRk9lI/csvdmnFCF1ICOwMYm+x0RUgxQ 7+YVq2PehLL91mwMhipLifw0TTlZvnS+nDFOFlkrmwC2GtJsskaWcxkN5bFAtuZJph vsjH+6F6NaDyA== Date: Tue, 4 Aug 2026 21:50:50 +0000 From: Yosry Ahmed To: "Vlastimil Babka (SUSE)" Cc: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Mike Rapoport , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sumit Garg , Will Deacon , rientjes@google.com, "Kalyazin, Nikita" , patrick.roy@linux.dev, "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 Message-ID: References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-19-6f5729aa9832@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: r8rtn85cdhnqqswxii6yznuee14dchjy X-Rspamd-Queue-Id: BC4DC80002 X-HE-Tag: 1785880253-206356 X-HE-Meta: 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 H8tS665d XINHo+XdCWuw95UUbDoqO0mvzVUJr2WSW1OM0Q5I1C1fyTXWK86S5hq+DBwuyKTH9zVFJApYwHkAViclUgAA0WWEs8zzSP27LNT9EnVzYU481aRAk7n3KNpPxtZinehdq/H5ctbHAsBNWINanZoBF7BUvE4M99i+PnbuksltdNRhuiGgFHe/hzKZqJA0BxnSrjBHeX7M9rXkqTOyxnU2ksKdFYezHoKOaHUMh4yJi4nVPB8H8hfXJLz22HcsoK6B11c6UccHY4ibRfekUqkOtbMWCZlV68TU+9mpz7FiaV4wLSKNw9huopczorSBIxOSB/0t+ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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_HIGH > > non-blocking allocations accesses reserves") renamed ALLOC_HARDER to > > ALLOC_NON_BLOCK because the former is "a vague description". > > > > However, vagueness is accurate here, this is a vague flag. It is not set > > for __GFP_NOMEMALLOC. It doesn't really mean "allocate without blocking" > > but rather "allow dipping into atomic reserves, _because_ of the need > > not to block". > > > > A later commit will need an alloc flag that really means "don't block > > here", so go back to the flag's old name and update the commentary > > to try and give it a slightly clearer meaning. > > > > Signed-off-by: Brendan Jackman > > I wonder if we need to do this, and instead we could repurpose > ALLOC_NON_BLOCK directly. AFAIU it's about removing the side-effect of > gfp_allowed_mask in the next patch. But what would happen if we did that > using the existing ALLOC_NON_BLOCK (or maybe just renamed to ALLOC_NOBLOCK?). > > - in __zone_watermark_ok(), ALLOC_NON_BLOCK could now be *not* set in > situations where previously it was set due to gfp_allowed_mask masking out > __GFP_DIRECT_RECLAIM. But it only has an effect on top of __GFP_HIGH (thus > ALLOC_MIN_RESERVE... which seems contradicting the ALLOC_NON_BLOCK > description comment btw). Also __GFP_DIRECT_RECLAIM is only masked out by > GFP_BOOT_MASK when all memory is free, so it's kinda moot? > > - in rmqueue_buddy() we allow access to highatomic reserves since > 281dd25c1a018. That commit describes GFP_ATOMIC so we could have been > checking ALLOC_MIN_RESERVE. But we can also leave this alone because it > doesn't actually matter when GFP_BOOT_MASK is set, as above. IIUC we are trying to find out if the callers either has interrupts disabled or is holding a lock, and using __GFP_DIRECT_RECLAIM as an indicator. As you mention, it seems like __GFP_DIRECT_RECLAIM is only masked during boot, presumably before we can allocate any unmapped memory (should always be user memory?). So maybe we should just use gfpflags_allow_blocking()? I also wonder if restricing to callers __GFP_DIRECT_RECLAIM is too restrictive, we can probably key off __GFP_ATOMIC as I assume any callers with IRQs disabled or wiht a lock have to set it. Maybe we can also use preemptible(), but that creates a dependency on CONFIG_PREEMPT_COUNT as far as I can tell.