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[2003:d8:2f27:6d00:7b96:afc9:83d0:5bd]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee07412111sm453030f8f.28.2025.09.17.12.05.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Sep 2025 12:05:47 -0700 (PDT) Message-ID: Date: Wed, 17 Sep 2025 21:05:44 +0200 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 v2] mm/memory-failure: Support disabling soft offline for HugeTLB pages To: Kyle Meyer Cc: Anshuman Khandual , akpm@linux-foundation.org, corbet@lwn.net, linmiaohe@huawei.com, shuah@kernel.org, tony.luck@intel.com, jane.chu@oracle.com, jiaqiyan@google.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 References: <8c3188da-7078-4099-973a-1d0d74db2720@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.09.25 20:51, Kyle Meyer wrote: > On Wed, Sep 17, 2025 at 09:02:55AM +0200, David Hildenbrand wrote: >> >>>> + >>>> + 0 - Enable soft offline >>>> + 1 - Disable soft offline for HugeTLB pages >>>> + >>>> +Supported values:: >>>> + >>>> + 0 - Soft offline is disabled >>>> + 1 - Soft offline is enabled >>>> + 3 - Soft offline is enabled (disabled for HugeTLB pages) >>> >>> This looks very adhoc even though existing behavior is preserved. >>> >>> - Are HugeTLB pages the only page types to be considered ? >>> - How the remaining bits here are going to be used later ? >>> >> >> What I proposed (that could be better documented here) is that all other >> bits except the first one will be a disable mask when bit 0 is set. >> >> 2 - ... but yet disabled for hugetlb >> 4 - ... but yet disabled for $WHATEVER >> 8 - ... but yet disabled for $WHATEVERELSE >> >>> Also without a bit-wise usage roadmap, is not changing a procfs >>> interface (ABI) bit problematic ? >> >> For now we failed setting it to values that are neither 0 or 1, IIUC >> set_enable_soft_offline() correctly? > > Yes, -EINVAL will be returned. > >> So there should not be any problem, or which scenario do you have in mind? > > Here's an alternative approach. > > Do not modify the existing sysctl parameter: > > /proc/sys/vm/enable_soft_offline > > 0 - Soft offline is disabled > 1 - Soft offline is enabled > > Instead, introduce a new sysctl parameter: > > /proc/sys/vm/enable_soft_offline_hugetlb > > 0 - Soft offline is disabled for HugeTLB pages > 1 - Soft offline is enabled for HugeTLB pages > > and note in documentation that this setting only takes effect if > enable_soft_offline is enabled. > > Anshuman (and David), would you prefer this? Hmm, at least I don't particularly like that. For each new exception we would create a new file, and the file has weird semantics such that it has no meaning when enable_soft_offline=0. -- Cheers David / dhildenb