From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4603A331222; Thu, 4 Dec 2025 20:58:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764881889; cv=none; b=n/alKROB6UoXIeYllG0wpT+DC03hrmFJ2x8ZAwrEOCnvjXGzFVkghF/W5DL6Xm7SBQtG04lCP5RpZelASNa8RKvJzBijmmBqMkZ/L2pXr5VQ61Ak4diWARV+gJfUK6jC+hjTp9uI91Wj6uVLh6Yimi0CjQC+L3m5s4g+87zAxRQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764881889; c=relaxed/simple; bh=loobrzi70Pz8tRGrBPxxU+Z3c+tNVIg/LFKhDULsEAI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qQlBQHTjSJFRmFLzlolgAMZFj+mHPAcl592tulT/AKB/1hPVAfELCTLHE3mPeuhVgfWwGiD18j7eQAv9gybac1Bn00Y55LL2EQ1zQvUfYaW2DlryAVrN1JZPLfkLsHY1OonAb8w9ZsmkwhzGxE1HVHekUvnT1tjajYMosq/ljsw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uClXz34X; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="uClXz34X" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65F3AC4CEFB; Thu, 4 Dec 2025 20:58:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764881888; bh=loobrzi70Pz8tRGrBPxxU+Z3c+tNVIg/LFKhDULsEAI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=uClXz34XPXMkEKff3YIWkBOZ37RSNuVgI+nxzOy4TOM+DZPFXJFT5LoRMPVzQVDB+ eGM6XD/mm14R4hH1LID2HzwVCSwnLVXazDKHDElM9jZdFe2JxumKbIvocccvJw7wPX SpavRLRZFhmxTuotit33kbMWKD3Jy9YkeXhOi9JHK2fZiONV1G26eNS58b05e1lX/M WkkyCucIFVM9KECbZuASEanszKlXzX74vlOX2t8FAWc163PSPTdmjRIRhB4TQtECbE XhqjHHjVFKU7pN+ZflKZPDUQdRq8mJjx1d3ZTOmZpCS1u3E39BiOePBI/xM0TBvqRB QPZLVe7hqQKnA== Message-ID: <48344838-d601-45ae-b260-01eb6b2fa422@kernel.org> Date: Thu, 4 Dec 2025 21:58:01 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm, hugetlb: implement movable_gigantic_pages sysctl To: Gregory Price 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 References: <20251203063836.187016-1-gourry@gourry.net> <305328e0-3011-409c-a040-76fc478d541a@kernel.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/4/25 18:14, Gregory Price wrote: > 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? >> > > It retries until a 1GB page is available. > > Example test: > > echo 0 > node0/hugepages/..-1GB/nr_hugepages (dram node) > echo 1 > node1/hugepages/..-1GB/nr_hugepages (zone_movable node) > ./alloc_huge & (allocate the page) > ./node1_offline & (offline > memory*/state) > sleep 5 (give offline time) > echo 1 > node0/hugepages/..-1GB/nr_hugepages (dram node) > > This node1_offline generates migration failures until the last step > occurs, at which point migration and node1_offline complete as expected. > > The migration failures produce the following: > > [ 707.443105] migrating pfn c080000 failed ret:-12 > [ 707.453353] page: refcount:2 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xc080000 > [ 707.471315] head: order:18 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0 > [ 707.488504] anon flags: 0x17ffff0000000848(uptodate|owner_2|head|node=1|zone=3|lastcpupid=0x1ffff) > [ 707.508393] page_type: f4(hugetlb) > [ 707.515940] raw: 17ffff0000000848 ffa000007d873cc0 ffa000007d873cc0 ff1100082366c6e9 > [ 707.533126] raw: 0000000000000000 0000000000000010 00000002f4000000 0000000000000000 > [ 707.550317] head: 17ffff0000000848 ffa000007d873cc0 ffa000007d873cc0 ff1100082366c6e9 > [ 707.567699] head: 0000000000000000 0000000000000010 00000002f4000000 0000000000000000 > [ 707.585085] head: 17ffff0000000012 ffd4000302000001 0000000000000000 0000000000000000 > [ 707.602469] head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000040000 > [ 707.619851] page dumped because: migration failure > > > I can add this to the changelog if you prefer Yes, we should document that. I guess it's just what we already document in the memory hotplug doc: it keeps retrying until there is sufficient free memory. -- Cheers David