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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766332165; bh=p++ab+scdeusI2vZJTjgYwM79xzmVgySoMmqEdRkErw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=EalTEbZhrGgrW+WpgUJ7P7k4WQW/3fCqLxM7be1fN7KjZbdOrmrXIU2zNbdexG8AT X9M0Xx59AFPBGRIBTvEyV/FLah2Fp52ZmYMCHcpORBjJpb19YZxl7tK5qYKxb7BwiE +WuDtoTYS4sIGkxyiPphIrapYgLBR3bgKpAXHTdJeAUMD8jm0mCOjXNETbAzDOh7Hz KoutTTWwFMp3JQg8l6XtGa9fP+JX+JF4lu1S77QJ/nn318DCYpWcDLdG4yMf1Np1mT c+21uigte7TXnEjX3e4IzAyoMEozEmjnHqDj+eiwIl9EOQi37usKkd1oNXPNRBTTK3 1brEb9KuoorRw== Message-ID: Date: Sun, 21 Dec 2025 16:49:17 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5] mm, hugetlb: implement movable_gigantic_pages sysctl To: Gregory Price , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com, 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, hannes@cmpxchg.org, Mel Gorman , David Rientjes References: <20251221125603.2364174-1-gourry@gourry.net> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251221125603.2364174-1-gourry@gourry.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C26CE14000B X-Stat-Signature: uzrqerwuhu9w1e9bgpumaq7ns5g3tizd X-Rspam-User: X-HE-Tag: 1766332166-285602 X-HE-Meta: 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 dppQLiB0 fX+Zeb/Gi5dPQ4u1J062oCh92mwTDnVl0nZ796yU/xY4hTNVJ9vYi45oLAkNjUgqa3w4e57HmRHw2JYYEFNLEetVunoleZ497TpZOqDya4bUdJ0bL3lpYNvWeRpoMMfogFUb4ezeN7KXvZPuHX4KITAAYmrf4P2TX9DAIE9ytgWQSW99ox/vXpq/c9fgpP2eF26thAkOVlp8ageGXYnEOcTQErBZ7gxzovWzcJytxk36A7rzKuPVZOMhzRmiUXcBXpayhGpzYLOeytb99P5I/aihclgWbWuPOaSEbktIA0DGqc+MibWzTGziHjsVu+xnvh7NDqGGvayU3s3n3H9Jgp1sTytdxdstiw0XfqkxHjOGVMhs5lhKUgLBx24v2yJO56jkO4lyHdFC3mgwIXxxdIXplBfw9Bxu/nbHjIR7gpSBXtmM48FShHaySP40T2xkq0CQ1QPwOyXx4+1fUdzl7tT4+R1t4rBklhU9bBgA5/THSII6eUfD2C79BqoR9cTlQ5Wybzh/pyVJu817fqqG9XXZy/GELwJgoz53e6OXGRsKKs24= 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 12/21/25 13:56, 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. > > However, since there are scenarios where gigantic pages are migratable, > we should allow use of these on movable regions. > > When not valid 1GB is available for migration, hot-unplug will retry > indefinitely (or until interrupted). For example: > > echo 0 > node0/hugepages/..-1GB/nr_hugepages # clear node0 1GB pages > echo 1 > node1/hugepages/..-1GB/nr_hugepages # reserve node1 1GB page > ./alloc_huge_node1 & # Allocate a 1GB page on node1 > ./node1_offline & # attempt to offline all node1 memory > echo 1 > node0/hugepages/..-1GB/nr_hugepages # reserve node0 1GB page > > In this example, node1_offline will block indefinitely until the final > step, when a node0 1GB page is made available. > > Note: Boot-time CMA is not possible for driver-managed hotplug memory, > as CMA requires the memory to be registered as SystemRAM at boot time. > Additionally, 1GB huge pages are not supported by THP. > > Cc: David Hildenbrand > Cc: Mel Gorman > Cc: Michal Hocko > Suggested-by: David Rientjes > Signed-off-by: Gregory Price > Link: https://lore.kernel.org/all/20180201193132.Hk7vI_xaU%25akpm@linux-foundation.org/ > --- Acked-by: David Hildenbrand (Red Hat) -- Cheers David