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[2003:cb:c716:3000:f155:cef2:ff4d:c7]) by smtp.gmail.com with ESMTPSA id z2-20020adff742000000b00326dd5486dcsm2790857wrp.107.2023.11.02.08.47.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Nov 2023 08:47:40 -0700 (PDT) Message-ID: <1e99ff39-b1cf-48b8-8b6d-ba5391e00db5@redhat.com> Date: Thu, 2 Nov 2023 16:47:38 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/1] mm: report per-page metadata information Content-Language: en-US To: Wei Xu , Pasha Tatashin Cc: Sourav Panda , corbet@lwn.net, gregkh@linuxfoundation.org, rafael@kernel.org, akpm@linux-foundation.org, mike.kravetz@oracle.com, muchun.song@linux.dev, rppt@kernel.org, rdunlap@infradead.org, chenlinxuan@uniontech.com, yang.yang29@zte.com.cn, tomas.mudrunka@gmail.com, bhelgaas@google.com, ivan@cloudflare.com, yosryahmed@google.com, hannes@cmpxchg.org, shakeelb@google.com, kirill.shutemov@linux.intel.com, wangkefeng.wang@huawei.com, adobriyan@gmail.com, vbabka@suse.cz, Liam.Howlett@oracle.com, surenb@google.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, Greg Thelen References: <20231101230816.1459373-1-souravpanda@google.com> <20231101230816.1459373-2-souravpanda@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 02.11.23 16:43, Wei Xu wrote: > On Wed, Nov 1, 2023 at 7:58 PM Pasha Tatashin wrote: >> >> On Wed, Nov 1, 2023 at 7:40 PM Wei Xu wrote: >>> >>> On Wed, Nov 1, 2023 at 4:08 PM Sourav Panda wrote: >>>> >>>> Adds a new per-node PageMetadata field to >>>> /sys/devices/system/node/nodeN/meminfo >>>> and a global PageMetadata field to /proc/meminfo. This information can >>>> be used by users to see how much memory is being used by per-page >>>> metadata, which can vary depending on build configuration, machine >>>> architecture, and system use. >>>> >>>> Per-page metadata is the amount of memory that Linux needs in order to >>>> manage memory at the page granularity. The majority of such memory is >>>> used by "struct page" and "page_ext" data structures. In contrast to >>>> most other memory consumption statistics, per-page metadata might not >>>> be included in MemTotal. For example, MemTotal does not include memblock >>>> allocations but includes buddy allocations. While on the other hand, >>>> per-page metadata would include both memblock and buddy allocations. >>> >>> I expect that the new PageMetadata field in meminfo should help break >>> down the memory usage of a system (MemUsed, or MemTotal - MemFree), >>> similar to the other fields in meminfo. >>> >>> However, given that PageMetadata includes per-page metadata allocated >>> from not only the buddy allocator, but also the memblock allocations, >>> and MemTotal doesn't include memory reserved by memblock allocations, >>> I wonder how a user can actually use this new PageMetadata to break >>> down the system memory usage. BTW, it is not robust to assume that >>> all memblock allocations are for per-page metadata. >>> >> >> Hi Wei, >> >>> Here are some ideas to address this problem: >>> >>> - Only report the buddy allocations for per-page medata in PageMetadata, or >> >> Making PageMetadata not to contain all per-page memory but just some >> is confusing, especially right after boot it would always be 0, as all >> struct pages are all coming from memblock during boot, yet we know we >> have allocated tons of memory for struct pages. >> >>> - Report per-page metadata in two separate fields in meminfo, one for >>> buddy allocations and another for memblock allocations, or >> >> This is also going to be confusing for the users, it is really >> implementation detail which allocator was used to allocate struct >> pages, and having to trackers is not going to improve things. >> >>> - Change MemTotal/MemUsed to include the memblock reserved memory as well. >> >> I think this is the right solution for an existing bug: MemTotal >> should really include memblock reserved memory. > > Adding reserved memory to MemTotal is a cleaner approach IMO as well. > But it changes the semantics of MemTotal, which may have compatibility > issues. I object. -- Cheers, David / dhildenb