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[2003:d8:2f20:da00:b70a:d502:3b51:1f2d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e774a3fb5bsm805305f8f.58.2025.09.12.00.53.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Sep 2025 00:53:03 -0700 (PDT) Message-ID: Date: Fri, 12 Sep 2025 09:53:02 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/memory-failure: Disable soft offline for HugeTLB pages by default To: "Luck, Tony" Cc: Kyle Meyer , akpm@linux-foundation.org, corbet@lwn.net, linmiaohe@huawei.com, shuah@kernel.org, Liam.Howlett@oracle.com, bp@alien8.de, hannes@cmpxchg.org, jack@suse.cz, jane.chu@oracle.com, jiaqiyan@google.com, 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: <749511a8-7c57-4f97-9e49-8ebe8befe9aa@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 11.09.25 19:56, Luck, Tony wrote: > On Thu, Sep 11, 2025 at 10:46:10AM +0200, David Hildenbrand wrote: >> On 10.09.25 18:15, Kyle Meyer wrote: >>> Soft offlining a HugeTLB page reduces the available HugeTLB page pool. >>> Since HugeTLB pages are preallocated, reducing the available HugeTLB >>> page pool can cause allocation failures. >>> >>> /proc/sys/vm/enable_soft_offline provides a sysctl interface to >>> disable/enable soft offline: >>> >>> 0 - Soft offline is disabled. >>> 1 - Soft offline is enabled. >>> >>> The current sysctl interface does not distinguish between HugeTLB pages >>> and other page types. >>> >>> Disable soft offline for HugeTLB pages by default (1) and extend the >>> sysctl interface to preserve existing behavior (2): >>> >>> 0 - Soft offline is disabled. >>> 1 - Soft offline is enabled (excluding HugeTLB pages). >>> 2 - Soft offline is enabled (including HugeTLB pages). >>> >>> Update documentation for the sysctl interface, reference the sysctl >>> interface in the sysfs ABI documentation, and update HugeTLB soft >>> offline selftests. >> >> I'm sure you spotted that the documentation for >> "/sys/devices/system/memory/soft_offline_pag" resides under "testing". > > But that is only one of several places in the kernel that > feed into the page offline code. Right, I can see one more call to soft_offline_page() from arch/parisc/kernel/pdt.c. And there is memory_failure_work_func() that I missed. So agreed that this goes beyond testing. It caught my attention because you ended up modifying documentation residing in Documentation/ABI/testing/sysfs-memory-page-offline. Reading 56374430c5dfc that Kyle pointed out is gets clearer. So the patch motivation/idea makes sense to me. I'll note two things: (1) The interface design is not really extensible. Imagine if we want to exclude yet another page type. Can we maybe add a second interface that defines a filter for types? Alternatively, you could use all the remaining flags as such a filter. 0 - Soft offline is completely disabled. 1 - Soft offline is enabled except for manually disabled types. Filter 2 - disable hugetlb. So value 3 would give you "enable all except hugetlb" etc. We could add in the future 4 - disable guest_memfd (just some random example) Then you 2) Changing the semantics of the value "1" IIUC, you are changing the semantics of value "1". It used to mean "SOFT_OFFLINE_ENABLED" now it is "SOFT_OFFLINE_ENABLED_SKIP_HUGETLB", which is a change in behavior. If that is the case, I don't think that's okay. 2) I am not sure about changing the default. That should be an admin/ distro decision. -- Cheers David / dhildenb