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[2003:cb:c71b:7900:8752:fae3:f9c9:a07e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43ec366aa29sm53303815e9.39.2025.04.04.12.07.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Apr 2025 12:07:24 -0700 (PDT) Message-ID: <427f683b-ac68-4820-b264-4016b34df592@redhat.com> Date: Fri, 4 Apr 2025 21:07:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] docs: update THP admin guide about non-tmpfs filesystem support To: Luis Chamberlain Cc: "Pankaj Raghav (Samsung)" , Andrew Morton , Jonathan Corbet , linux-kernel@vger.kernel.org, willy@infradead.org, linux-mm@kvack.org, Bagas Sanjaya , da.gomez@kernel.org, gost.dev@samsung.com, linux-doc@vger.kernel.org, Pankaj Raghav References: <20250404140657.29285-1-kernel@pankajraghav.com> <09c13770-4d62-430a-827d-6ad35411d18c@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Vdt1DQDthNoxzMp5gaj2Yb3cuOTB3lhLLhYU7m7Yexc_1743793645 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7EA56100007 X-Stat-Signature: 3gkexyyipe3u8pn1egx6ha3o39w1bxo4 X-HE-Tag: 1743793648-364555 X-HE-Meta: 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 Sw5yc0Sb DAs1pfDJj6dR+GrzAHkNwdoYWbeNm0o3UtO2FBmyQeF9TnBSxvw1VM6x2HG2yAd1GBTpSfQo+keA5e318D/Z/EPM+68Sy37gBgOcjn7IX/RAU7iF7McC+8KCEeR28nPyHLMwAD9fVMKOtEhE4iQ+6iA2remZYaubJacp8snUyEy2ahZ7FBq59AQa2ke3HiNM2KE/wrjvMDTiPhAJFGks+aQKaY2/2RNqNmpXRmv2wJ2gCMqp4vD3HdLpAx8kCrBFlb4y7VHmIEJO1tP85DUFW+hEMPNeqDluZmwZmtj6MsrcnwPasYP4HREdMy0ef/3U5stm7EpzBygCILHpglUHXk75seNXqlyEerW4s/y435+VsDkyHyUNJiLiNoi9zOU77iAt452+UkkqCmtfw1Rvy0COkZKdnrzkIyZuRUzUzotqBHfulT96Sj5IIxCkudjJ9Rx+XR5fhE0V7iEw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 04.04.25 19:58, Luis Chamberlain wrote: > On Fri, Apr 04, 2025 at 06:18:12PM +0200, David Hildenbrand wrote: >> On 04.04.25 17:32, Luis Chamberlain wrote: >>> On Fri, Apr 04, 2025 at 04:06:57PM +0200, Pankaj Raghav (Samsung) wrote: >>>> From: Pankaj Raghav >>>> >>>> THP support for non-tmpfs filesystem has been around for some time now. >>>> Update the admin guide to reflect it. >>>> >>>> While we are at it, move FilePmdMapped to previous paragraph for clarity, >>>> and clarify ShmemPmdMapped & ShmemHugePage. >>>> >>>> Signed-off-by: Pankaj Raghav >>>> Acked-by: David Hildenbrand >>>> --- >>>> >>>> Changes since v2: >>>> - Address comment from Bagas Sanjaya >>>> - Squash commits and Ack from David >>>> >>>> Documentation/admin-guide/mm/transhuge.rst | 22 +++++++++++++++------- >>>> 1 file changed, 15 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst >>>> index dff8d5985f0f..f8aae64e38d0 100644 >>>> --- a/Documentation/admin-guide/mm/transhuge.rst >>>> +++ b/Documentation/admin-guide/mm/transhuge.rst >>>> @@ -12,8 +12,8 @@ using huge pages for the backing of virtual memory with huge pages >>>> that supports the automatic promotion and demotion of page sizes and >>>> without the shortcomings of hugetlbfs. >>>> -Currently THP only works for anonymous memory mappings and tmpfs/shmem. >>>> -But in the future it can expand to other filesystems. >>>> +Currently, THP only works for anonymous memory mappings, tmpfs/shmem and >>>> +filesystems that support large folios. >>> >>> That seems to allude that THP can be supported on filesystems >>> that suppor large folios. I don't think we want to call that THP >>> and that can confuse folks. Leaving "currently" also seems to >>> indicate that there is more work to be done for THP for filesystems >>> but that's not true as well. So how about something like: >>> >>> THP only works for anonymous memory mappings, and the tmpfs/shmem is the only >>> filesystem to support it. The alternative to THP for other filesystems is to >>> support large folios and with it you can end up using huge pages >> >> That makes things more complicated without a good reason. >> >> See CONFIG_READ_ONLY_THP_FOR_FS as an early usage of the term "THP" for >> stuff we have in the pagecache. > > OK. > >> (with large folios we now properly implement >> this concept, and support more than only PMD size) > > Do we really want to call large folio support on filesystems THP? Good question. "folio" is just the metadata we currently use to manage a chunk of memory, and a "large folio" is one that spans more than a single page -- huge page, large page, super page, ... in the past the metadata for that used to be a complicated piece of "compound page". In the future, we might call it differently (struct file_mem ?), who knows. So "large folio" support in a fs allows for the usage of these larger chunks of memory (huge pages). The filesystem tries to transparently make use of huge pages (of various sizes); in contrast to hugetlb, that is "transparent" in a way that these can be split, partially mapped, partially truncated -- just like for anon or shmem. (Well, the "transparent" part was never really 100% true, but that's a different story) I see more similarity with THP than with hugetlb in that sense. In the end I don't think the terminology matters that much -- note that we are talking about an admin guide that resides in transhuge.rst -- as long as people don't confuse it with "ordinary" huge pages as in hugetlb. "file huge page" is rather misleading. I'd be curious in which sense these file thingies are different than what we have for anon/shmem/... except that some toggles don't apply to them and the pagecache mostly "more transparently" makes use of them. (which makes them even more transparent? ;) ) -- Cheers, David / dhildenb