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b=l6l6g97ftKGETwe9W+MgWjB7StxSM/rVyuw87s1BGU7VPUbP4jpcnKr+cLkBw1ym4 2fFxA8DyzSMtnmtuppQVDmKr2v60BVjWnZ9wwNmhttPQfkgNceKO6BjypqhXsEkHwe x5s/RRZgYbPhDo/ygFvmqmqWAP7Lmv1wVCBrtn4LDqBFKPRsGdZFBM5rB1Q1ztxo9f LSUvmic9nHXt8/ZyZG4fdyAy1iqul0fJd4do3I3sPN0C92jftCAGhHw0gXpglGLLJF 7f6jS0ePCDTOhaVGFBvmoBRhtmZHHfoNPyo//JqpZCvvSutgP5vz5wYWa2JKdIf+NB YMfPInhXkqAEA== Message-ID: <3126db67-8ac8-4913-bd4a-4008de730148@kernel.org> Date: Thu, 29 Oct 2026 10:49:54 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: page_alloc: do not give all non-blocking requests reserve access Content-Language: en-US To: Johannes Weiner , Andrew Morton Cc: Matthew Wilcox , Salvatore Dipietro , Christoph Hellwig , Dave Chinner , Matt Fleming , Mel Gorman , Michal Hocko , Suren Baghdasaryan , Brendan Jackman , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko , stable@vger.kernel.org References: <20261028171719.2043421-1-hannes@cmpxchg.org> <20261028171719.2043421-2-hannes@cmpxchg.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 239E01A0006 X-Stat-Signature: y3shw4jz4h96rznn9844hc1wpsztozrh X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793267401-16947 X-HE-Meta: U2FsdGVkX195jCmLoxKLK+t8XlFm1HHD/h71QKxluCtIibNDl24VYL3U2m9pbwE9SRSXf7A2Ia3PgAfHQS3Ibc2TwgpiJVMfx7cBrDLACVrgJavuWbCFotR5RSxzXovvmGwN9o7uqUZnkTzm6+QvuK9rAAa3THH9cEO48s5wVKXkqH57qbGtwz/wNM8U7lg8+0tKSpDjDGnPPbR3OLFH7wnN9sXC1uDyF+aW/p0XelpL3uMKBR24D5G3TT7hRtCPzVEe0R/T1aalV820XCq5fARhjaln4YMMTQLsSKhGUHcmuD7PJayFfe49yVM2bRvabzP18OzseT3aOofReQ26qrDYfXaOE4xbZc/0mYSTvU36j7A4EGmns/ubjljfwnGJWW0GK3laxWGC4bu3QWwf4OWjhLp8zzreC2C+2j6wzfr6ojNPZz/o9sYncZqkmDaPURDLDVcS0GRXkK/h6liwKXlW79yZcyoU3jFFt/Cwg8DOF/+vHyLLh9afEsb5mdSB8Z5icpdc5EZOUAQNQIogfN9zSJfd5peduhY+wH31Ltcc6zHhVLy4AKwYfWaA/9/g8sjJIrmZeWaiZogKxuWNDYIrHn/f4plxKGBdG1esdP/fBzcOdBaHQKrGQaTzK9FHWRZAz6HU21jQxkqhSlm9OKTKsd5jnd8wkusZzrduAkPO9z44PMd/H9M2LJLg2yPKY6qy2zokExV6WoJK0OCP+4g+7LmNwzGU8s/LC4iEJhYkU9YkpyyVAdx1jhiBl3weX2XKaAMVodYYKbUAaF4OMrvUc4ZIj0Lzzhf3JbDy3ASCBppCYDu3fvSgqhHwokbmRYIdN3JAg712woCkmY3LJXI168W6uczKsD8O+XbhsCI+R2VChZkuzOEPRyKjHZYoRCDftJ00UawN24eSg6V8sdjzWln0Y1jnFjaA5xwVPz43O4oczW6x5NdwE5os30GaIJQEOKIpPuOvXh/3qys /4swFhdL 1x+FHWDnOnJ9OCDnFqV6PRm4e0udMT/YRC0J04UtwUbusLK1UFmyhMxcEU6xsbpPb8/um708DPeJRokOI7hsZWy/S1fnlRpL1YVzZ1lddwZUkD0EUZLqSkffGISjdCWjs5PGFC9IUGjlgS2mcjSOOYZ1RvV46UkKHXLSFdpWSMCkBfl10bAhKNWS0QdixyVp9kN5l0NzLbnyqwkL3n0QebXijHHVjo7G726wrmUuF814xzSM9Ew6F4EYMjBy/p5Y49mUTMYSSK/sXQ4hvaEQZ4+Tyx+IZyVsgqF4e2xssoGd70qsc+/jDegw2zPRA1KyZopayJWrE0vL6mdYr33Ks8hd233Eih0/QLAuK414AvwSY8kp6l8AYDuZUBCtZFn3g4x2QJnP/5JOb1lLglubOsJc+FYjOOTJjD4lnt6BdXsWptHPySPHyAuSPEJILFz135gAW Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/28/26 18:15, Johannes Weiner wrote: > 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access > highatomic reserves") accidentally gave all non-blocking allocation > requests access to highatomic reserves, which includes GFP_NOWAIT and > other sites clearing __GFP_DIRECT_RECLAIM. > > While this improved atomic request success rate, it's unintentionally > broad and can actually worsen highatomic requests by squandering the > reserves on requests that don't need it. > > There are concurrent efforts to clear __GFP_DIRECT_RECLAIM altogether > for costly order __GFP_NORETRY requests, which would then also fall > into this exemption and deplete reserves even faster. > > What GFP_ATOMIC has over the others is __GFP_HIGH, which > alloc_flags_slowpath() translates to ALLOC_MIN_RESERVE. > > Narrow the exemption to contexts that have both ALLOC_NON_BLOCK | > ALLOC_MIN_RESERVE. > > Reported-by: Sashiko > Link: https://sashiko.dev/#/patchset/20260904115629.3993331-1-dipiets@amazon.it > Fixes: 281dd25c1a01 ("mm/page_alloc: let GFP_ATOMIC order-0 allocs access highatomic reserves") > Cc: stable@vger.kernel.org > Signed-off-by: Johannes Weiner Reviewed-by: Vlastimil Babka (SUSE) > --- > mm/page_alloc.c | 4 +++- > mm/page_alloc.h | 3 +++ > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index a8cac5e01066..8ac2e2bf14fc 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3238,7 +3238,9 @@ struct page *rmqueue_buddy(struct zone *preferred_zone, struct zone *zone, > * reserves as failing now is worse than failing a > * high-order atomic allocation in the future. > */ > - if (!page && (alloc_flags & (ALLOC_OOM|ALLOC_NON_BLOCK))) > + if (!page && > + ((alloc_flags & ALLOC_OOM) || > + (alloc_flags & ALLOC_MASK_ATOMIC) == ALLOC_MASK_ATOMIC)) > page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC); > > if (!page) { > diff --git a/mm/page_alloc.h b/mm/page_alloc.h > index e238ee91ed24..9c3c2830acb0 100644 > --- a/mm/page_alloc.h > +++ b/mm/page_alloc.h > @@ -60,6 +60,9 @@ > /* Flags that allow allocations below the min watermark. */ > #define ALLOC_RESERVES (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE|ALLOC_HIGHATOMIC|ALLOC_OOM) > > +/* Flags that mean GFP_ATOMIC */ > +#define ALLOC_MASK_ATOMIC (ALLOC_NON_BLOCK|ALLOC_MIN_RESERVE) > + > /* > * Structure for holding the mostly immutable allocation parameters passed > * between functions involved in allocations, including the alloc_pages*