From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 BC2C139C632; Thu, 18 Jun 2026 08:32:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781771525; cv=none; b=Re/ZsUoBwyGHcSpTzCyy62Htre/L9iSI9uKoOHThNWCB51uTlxk16HUdAALIwBfc/+LlFRQzjC/qFr843X9WmmOl8tuDzVYUjwOylnmW7VZgN4FNiWofIQ+BXLuwPoElLHwvm/ktUfimLgd+E9ExOINdLKgReqbJxpWJWStUElw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781771525; c=relaxed/simple; bh=uNgb/SC4s+Cl8BiN4hC5BHdxJV6aYS6e0CFl5/hOr/g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=exaGBCCQ/d73/gzc8nnkSGLRUO7N4MEt/VX9Sk/xzhFQuttzv0gqbFr66TzkmPwliKyLavUFqjim0Fl0hyve8vO/n1BWq17HoojkY88HAZlBmLnDVoJKyjJHdHneM0/a6XdicRU0Hp3c2u9kZY1yNO5c+t54/s0yuUfQ2g8tLhg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=j2jEFGPE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="j2jEFGPE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C766C1F000E9; Thu, 18 Jun 2026 08:31:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781771524; bh=A7kSk5FOjjwX9qzkYqIYgCSl9ULz2D77J4Nkg6zht44=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=j2jEFGPEWL9lzxkVGCvnNtZYdbh7pxmtdsBZwXn6+iEb0YuIKU7gTgPF6WKXSMfp4 usaZPHg+k9PxJ0wAYkulqzXk31waexQkXRLEwIWdUVQnZFCvBGrGmf343JfRuxW7GB jwE+289txwb9YxL3a1PLpPC6RVeUuhOEMpEtg54JLPSSZmbWQ5r6Dr0VD0esXw3ca8 4B654DM+7BOAjc70LM74Awq64aIXg7mwchJeowJwxVqVcjnL/VbBUzAT447veLzEop 5CHYhmBx8ajvlM2jn1CLZZRHtPfG4RQi7JfZkNcekAHGj/r0KeQOrQkWhCUjYdW6H/ lePv65VCIFDpg== Message-ID: <48c80176-369d-40e1-bf6b-1cc72483a8da@kernel.org> Date: Thu, 18 Jun 2026 10:31:46 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC][RFC PATCH v4 00/27] Private Memory Nodes (w/ Compressed RAM) To: Gregory Price , Brendan Jackman Cc: "Vlastimil Babka (SUSE)" , Balbir Singh , lsf-pc@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, damon@lists.linux.dev, kernel-team@meta.com, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, dave@stgolabs.net, jonathan.cameron@huawei.com, dave.jiang@intel.com, alison.schofield@intel.com, vishal.l.verma@intel.com, ira.weiny@intel.com, dan.j.williams@intel.com, longman@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, osalvador@suse.de, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, yury.norov@gmail.com, linux@rasmusvillemoes.dk, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, jackmanb@google.com, sj@kernel.org, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, muchun.song@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, jannh@google.com, linmiaohe@huawei.com, nao.horiguchi@gmail.com, pfalcato@suse.de, rientjes@google.com, shakeel.butt@linux.dev, riel@surriel.com, harry.yoo@oracle.com, cl@gentwo.org, roman.gushchin@linux.dev, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, zhengqi.arch@bytedance.com, terry.bowman@amd.com, Matthew Wilcox References: <9f1815b0-896b-44ab-9e6d-9316d8f11033@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/16/26 15:47, Gregory Price wrote: > On Tue, Jun 16, 2026 at 11:57:42AM +0000, Brendan Jackman wrote: >> On Mon Jun 15, 2026 at 2:38 PM UTC, Vlastimil Babka (SUSE) wrote: >>> >>> I think the memalloc approach is dangerous due to unexpected nesting. There >>> might be nested page allocations in page allocation itself (due to some >>> debugging option). But also interrupts do not change what "current" points >>> to. Suddenly those could start requesting folios and/or private nodes and be >>> surprised, I'm afraid. >> >> Minor side-note: couldn't we just define it such that the allocator >> ignores the context when not in_task() (and warn if you try to enter the >> context while not currently in_task())? >> >> (Don't think this would change the conclusion very much, e.g. doesn't >> help with the nesting issues. Mostly curious in case I'm missing a >> detail here). >> So I took a look at which nested allocations we could end up having, and I wonder whether gfp_nested_mask() indicates all these? If we could reliably identify them, all we'd have to do is safe+restore some context (activating a "nested" context). > > I looked at this - only solves one issue and oh boy is that an obtuse > confusing condition to understand. We still suffer from recursion in > reclaim. Right, we'd have to clear the context before calling into reclaim/compaction that does weird things. I'm sure BPF hooks could just arbitrarily try to allocate pages with kmalloc_nolock(). So that would require a context save/restore as well. -- Cheers, David