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[109.81.86.254]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-45b7e8966acsm25768415e9.17.2025.08.28.23.41.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Aug 2025 23:41:16 -0700 (PDT) Date: Fri, 29 Aug 2025 08:41:15 +0200 From: Michal Hocko To: Thadeu Lima de Souza Cascardo Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Brendan Jackman , Johannes Weiner , Zi Yan , Mel Gorman , kernel-dev@igalia.com, Helen Koike , Matthew Wilcox , NeilBrown , Thierry Reding Subject: Re: [PATCH] mm/page_alloc: only set ALLOC_HIGHATOMIC for __GPF_HIGH allocations Message-ID: References: <20250814172245.1259625-1-cascardo@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250814172245.1259625-1-cascardo@igalia.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: DAF3E1C000F X-Stat-Signature: 6pzterecak53w3dyzifr9eumyqcixo5i X-Rspam-User: X-HE-Tag: 1756449678-784046 X-HE-Meta: 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 Qnf8NanF 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 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 Thu 14-08-25 14:22:45, Thadeu Lima de Souza Cascardo wrote: > Commit 524c48072e56 ("mm/page_alloc: rename ALLOC_HIGH to > ALLOC_MIN_RESERVE") is the start of a series that explains how __GFP_HIGH, > which implies ALLOC_MIN_RESERVE, is going to be used instead of > __GFP_ATOMIC for high atomic reserves. > > Commit eb2e2b425c69 ("mm/page_alloc: explicitly record high-order atomic > allocations in alloc_flags") introduced ALLOC_HIGHATOMIC for such > allocations of order higher than 0. It still used __GFP_ATOMIC, though. > > Then, commit 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH > non-blocking allocations accesses reserves") just turned that check for > !__GFP_DIRECT_RECLAIM, ignoring that high atomic reserves were expected to > test for __GFP_HIGH. > > This leads to high atomic reserves being added for high-order GFP_NOWAIT > allocations and others that clear __GFP_DIRECT_RECLAIM, which is > unexpected. Later, those reserves lead to 0-order allocations going to the > slow path and starting reclaim. > > >From /proc/pagetypeinfo, without the patch: > > Node 0, zone DMA, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 > Node 0, zone DMA32, type HighAtomic 1 8 10 9 7 3 0 0 0 0 0 > Node 0, zone Normal, type HighAtomic 64 20 12 5 0 0 0 0 0 0 0 > > With the patch: > > Node 0, zone DMA, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 > Node 0, zone DMA32, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 > Node 0, zone Normal, type HighAtomic 0 0 0 0 0 0 0 0 0 0 0 > > Fixes: 1ebbb21811b7 ("mm/page_alloc: explicitly define how __GFP_HIGH non-blocking allocations accesses reserves") > Signed-off-by: Thadeu Lima de Souza Cascardo > Tested-by: Helen Koike > Cc: Mel Gorman > Cc: Michal Hocko > Cc: Matthew Wilcox > Cc: NeilBrown > Cc: Thierry Reding > Cc: Vlastimil Babka Yes, this makes a lot of sense to me. GFP_NOWAIT allocations should be opportunistic and quick to fail rather than dipping into memory reserves. We must have overlooked that during the review. Acked-by: Michal Hocko > --- > mm/page_alloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 2ef3c07266b3..bf52e3bef626 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4219,7 +4219,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask, unsigned int order) > if (!(gfp_mask & __GFP_NOMEMALLOC)) { > alloc_flags |= ALLOC_NON_BLOCK; > > - if (order > 0) > + if (order > 0 && (alloc_flags & ALLOC_MIN_RESERVE)) > alloc_flags |= ALLOC_HIGHATOMIC; > } > > -- > 2.47.2 -- Michal Hocko SUSE Labs