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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4efd3437a5fsm110792271cf.27.2025.12.03.01.36.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Dec 2025 01:36:04 -0800 (PST) Date: Wed, 3 Dec 2025 04:36:02 -0500 From: Gregory Price To: "David Hildenbrand (Red Hat)" Cc: linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, osalvador@suse.de, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, muchun.song@linux.dev, Mel Gorman , Alexandru Moise <00moses.alexander00@gmail.com>, David Rientjes Subject: Re: [PATCH v3] mm, hugetlb: implement movable_gigantic_pages sysctl Message-ID: References: <20251203063836.187016-1-gourry@gourry.net> <305328e0-3011-409c-a040-76fc478d541a@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <305328e0-3011-409c-a040-76fc478d541a@kernel.org> On Wed, Dec 03, 2025 at 10:26:20AM +0100, David Hildenbrand (Red Hat) wrote: > On 12/3/25 07:38, Gregory Price wrote: > > This reintroduces a concept removed by: > > commit d6cb41cc44c6 ("mm, hugetlb: remove hugepages_treat_as_movable sysctl") > > > > This sysctl provides flexibility between ZONE_MOVABLE use cases: > > 1) onlining memory in ZONE_MOVABLE to maintain hotplug compatibility > > 2) onlining memory in ZONE_MOVABLE to make hugepage allocate reliable > > > > When ZONE_MOVABLE is used to make huge page allocation more reliable, > > disallowing gigantic pages memory in this region is pointless. If > > hotplug is not a requirement, we can loosen the restrictions to allow > > 1GB gigantic pages in ZONE_MOVABLE. > > > > Since 1GB can be difficult to migrate / has impacts on compaction / > > defragmentation, we don't enable this by default. Notably, 1GB pages > > can only be migrated if another 1GB page is available - so hot-unplug > > will fail if such a page cannot be found. > > In light of the other discussion: will it fail or will it simplt retry > forever, until there is a free 1g page? > ... > > +- When an admin sets the ``movable_gigantic_pages`` sysctl to true, gigantic > > + pages are allowed in ZONE_MOVABLE. This only allows migratable gigantic > > + pages to be allocated; however, if there are no eligible destination gigantic > > + pages at offline, the offlining operation will fail. > > Same question here. > Hah, great question. I will make a note to try this in the morning. > Nothing else jumped at me, in general as discussed, as long as it is opt-in > behavior > > Acked-by: David Hildenbrand (Red Hat) > > -- > Cheers > > David