From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 24E5C20C477; Thu, 5 Mar 2026 13:32:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772717579; cv=none; b=JQBwTD3xU0k9DPnlH/fraYHbeg9HD3Zk6geyBg9K7jPaMmW2GMVYPNKxzAkea8sjyketTf3Kvo2ETm+dNqjdwmxQJQ2B6shqOTq+JZvm+JqrYyGuLKnGcmB+0gDtRYCouvaDdKqNPTRC7kQfsmcb0rkPukr/auBVHb6xbJ9PW7o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772717579; c=relaxed/simple; bh=siCDPUyJkhmZJ+Z9bW2VgMjcMK37fNr6QVsSBWZ4794=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hvSdZC7jRIHLKu5evGLyzpNTucqCjX3KO8tL2AAOIpFBbPlLTm0E45V7NLuH70sNZK/fCHirZ9WxJ3b+hT7SZue3CBFitos5NTCepqwxGMZQKEiP/tMoTzuTKm9+RIoJmztYH4ksp44GuYa3l1HLE35zG8KRoYAyorGEu+wA310= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RPcRkrdS; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RPcRkrdS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 549B7C116C6; Thu, 5 Mar 2026 13:32:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772717578; bh=siCDPUyJkhmZJ+Z9bW2VgMjcMK37fNr6QVsSBWZ4794=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RPcRkrdSnQlgCCOm5dAW5evRzE0anV8F9AUk+zy5lNaC77Dl99PL+duuKShSHMr6N AazFdGtXtGiyPBV+5aB2O0MiW3P7yUIX0K2npXhP0JzEtDR9u9IQu3d4Le8xuYP1Xm mLIbPNMUQrHuulR3FkDQ1XCh12+/TvxwgrNSuw4kQzKLepia6V9DjiKKzKsFJS6WU4 5ocJPdt8T5wzYdBN8vOvKqYPOdZE81PryU7nwQgbSWzTLfyXK77kh7gWtvHXSKSYaK cyC7uUqY+lTXrzPFhAbHr6DTZ3DzgKdaAgvOF9Q7HHD7K0Gy3LEtpB2ebfs6Ij+mZq +49fFjmPcKjIQ== Message-ID: Date: Thu, 5 Mar 2026 14:32:49 +0100 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 v1] docs: filesystems: clarify KernelPageSize vs. MMUPageSize in smaps To: "Lorenzo Stoakes (Oracle)" Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Dev Jain , Barry Song , Lance Yang , Jonathan Corbet , Shuah Khan , Usama Arif , Andi Kleen References: <20260304155636.77433-1-david@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit > > Ah wait you dedicate a whole paragraph after this to tha :) Correct :) > >> +mapping that is currently resident in RAM (RSS); the process's proportional >> +share of this mapping (PSS); and the number of clean and dirty shared and >> +private pages in the mapping. >> + >> +Historically, the "KernelPageSize" always corresponds to the "MMUPageSize", >> +except when a larger kernel page size is emulated on a system with a smaller > > NIT: is -> was, as historically implies past tense. > > But it's maybe better to say: > > +Historically, the "KernelPageSize" has always corresponded to the "MMUPageSize", > > And: > > +except when a larger kernel page size is being emulated on a system with a smaller > Given that the PPC64 thingy still exists in the tree, I'll probably do: "KernelPageSize" always corresponds to "MMUPageSize", except when a larger kernel page size is emulated on a system with a smaller page size used by the MMU, which is the case for some PPC64 setups with hugetlb. >> +page size used by the MMU, which was the case for PPC64 in the past. >> +Further, "KernelPageSize" and "MMUPageSize" always correspond to the > > NIT: Further -> Furthermore > Helpful. >> +smallest possible granularity (fallback) that could be encountered in a > > could be -> can be > > Since we are really talking about the current situation, even if this, is > effect, a legacy thing. > >> +VMA throughout its lifetime. These values are not affected by any current >> +transparent grouping of pages by Linux (Transparent Huge Pages) or any > > 'transparent grouping of pages' reads a bit weirdly. > > Maybe simplify to: > > +These values are not affected by Transparent Huge Pages being in effect, or any... Works for me. > >> +current usage of larger MMU page sizes (either through architectural > > NIT: current usage -> usage Ack. > >> +huge-page mappings or other transparent groupings done by the MMU). > > Again I think 'transparent groupings' is a bit unclear. Perhaps instead: > > +huge-page mappings or other explicit or implicit coalescing of virtual ranges > +performed by the MMU). I'd assume the educated reader does not know what "explicit/implicit coalescing" even means, but works for me. :) > > ? > >> +"AnonHugePages", "ShmemPmdMapped" and "FilePmdMapped" provide insight into >> +the usage of some architectural huge-page mappings. > > Is 'some' necessary here? Seems to make it a bit vague. I had PUDs in mind. I can just call it "PMD-level architectural ..." > >> >> The "proportional set size" (PSS) of a process is the count of pages it has >> in memory, where each page is divided by the number of processes sharing it. >> @@ -528,10 +541,14 @@ pressure if the memory is clean. Please note that the printed value might >> be lower than the real value due to optimizations used in the current >> implementation. If this is not desirable please file a bug report. >> >> -"AnonHugePages" shows the amount of memory backed by transparent hugepage. >> +"AnonHugePages", "ShmemPmdMapped" and "FilePmdMapped" show the amount of >> +memory backed by transparent hugepages that are currently mapped through >> +architectural huge-page mappings (PMD). "AnonHugePages" corresponds to memory > > 'mapped through architectural huge-page mappings (PMD)' reads a bit strangely to > me, > > Perhaps 'mapped by transparent huge pages at a PMD page table level' instead? > I'll simplify to "mapped by architectural huge-page mappings at the PMD level" >> +that does not belong to a file, "ShmemPmdMapped" to shared memory (shmem/tmpfs) >> +and "FilePmdMapped" to file-backed memory (excluding shmem/tmpfs). >> >> -"ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by >> -huge pages. >> +There are no dedicated entries for transparent huge pages (or similar concepts) >> +that are not mapped through architectural huge-page mappings (PMD). > > similarly, perhaps better as 'are not mapped by transparent huge pages at a PMD > page table level'? I'll similarly call it "mapped by architectural huge-page mappings at the PMD level" Thanks a bunch! -- Cheers, David