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Wed, 17 Sep 2025 21:39:12 +0000 (GMT) Received: from p1lg14886.dc01.its.hpecorp.net (unknown [10.119.18.237]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by p1lg14878.it.hpe.com (Postfix) with ESMTPS id 0A89D130D6; Wed, 17 Sep 2025 21:39:11 +0000 (UTC) Received: from HPE-5CG20646DK.localdomain (unknown [16.231.227.36]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by p1lg14886.dc01.its.hpecorp.net (Postfix) with ESMTPS id 1A621804CDB; Wed, 17 Sep 2025 21:39:08 +0000 (UTC) Date: Wed, 17 Sep 2025 16:39:01 -0500 From: Kyle Meyer To: "Luck, Tony" Cc: Jiaqi Yan , David Hildenbrand , Anshuman Khandual , akpm@linux-foundation.org, corbet@lwn.net, linmiaohe@huawei.com, shuah@kernel.org, jane.chu@oracle.com, Liam.Howlett@oracle.com, bp@alien8.de, hannes@cmpxchg.org, jack@suse.cz, joel.granados@kernel.org, laoar.shao@gmail.com, lorenzo.stoakes@oracle.com, mclapinski@google.com, mhocko@suse.com, nao.horiguchi@gmail.com, osalvador@suse.de, rafael.j.wysocki@intel.com, rppt@kernel.org, russ.anderson@hpe.com, shawn.fan@intel.com, surenb@google.com, vbabka@suse.cz, linux-acpi@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm/memory-failure: Support disabling soft offline for HugeTLB pages Message-ID: References: <8c3188da-7078-4099-973a-1d0d74db2720@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; 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Given /proc/sys/vm/enable_soft_offline is extensible, I would > > prefer a compact userspace API. > > > > > would create a new file, and the file has weird semantics such that it > > > has no meaning when enable_soft_offline=0. > > So the expand the bitmask idea from earlier in this thread? > > Bit0 0 = soft offline disabled. 1 = Enabled (but see other bits) > Bit1 0 = allow offline of 4K pages, 1 = suppress 4K offline > Bit2 0 = allow offline of hugetlb, 1 = suppress hugetlb offline > Bit3 0 = allow breakup of transparent huge pages to just offline 4K, 1 = suppress transparent breakup > Bit4+ Reserved for suppressing other page types we invent in the future > > Values 0 and 1 keep their original meaning. > > Value 5 means: offline 4K, keep hugetlb, breakup transparent huge pages. Do you happen to have any use cases or reasoning for why someone might want to disable soft offline for 4K pages or transparent huge pages? I'd like to understand the motivation for adding the extra bits. Thanks, Kyle Meyer