From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BC4D9CA1002 for ; Thu, 4 Sep 2025 10:31:43 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E20AD8E0011; Thu, 4 Sep 2025 06:31:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DF86E8E0001; Thu, 4 Sep 2025 06:31:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D0DE08E0011; Thu, 4 Sep 2025 06:31:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id C0E858E0001 for ; Thu, 4 Sep 2025 06:31:42 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 6A7D25C665 for ; Thu, 4 Sep 2025 10:31:42 +0000 (UTC) X-FDA: 83851201644.03.CB52B85 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf30.hostedemail.com (Postfix) with ESMTP id F1A5F80007 for ; Thu, 4 Sep 2025 10:31:39 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=BVvLsySn; spf=pass (imf30.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1756981900; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=iNez6/M9s3PJsme5pRqUUeFXGJSz6E2jhwKDhn5HC94=; b=lZrgYOnfjLQOovx7FHkhP2ALHA8ktqaexM35Mqa7FZy+oUSMEbGV/vx1tCgyEe99r7Wqjd 9an711BsUhp/AfRcYmqdohhOwFN6pXjsocM21fCRWDYTK2ExgPheRz0bYjrcTa3dwXIFXS 0sTD0LyHKN4iGLb6L5ABqiu5Rcpg40o= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=BVvLsySn; spf=pass (imf30.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1756981900; a=rsa-sha256; cv=none; b=3ifSc5HFTgX3h8C1LuT9MPdcL3sKaip9soLmVR0uUHEneoKcwsuewaRv3RCLkLBLRejxRV pjOFADnDfOsia/IFpBzdatQKz/b41+mUC+kpynXuzHnXQywKQT0D9d2rLNRWsfTu7K9oxM +GoyZkNrJuoqiFp+OyNqzk7MIjVxSTM= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1756981899; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=iNez6/M9s3PJsme5pRqUUeFXGJSz6E2jhwKDhn5HC94=; b=BVvLsySn2Hwf6rXwH2Z9ZUCK+yYkU+jYQ9gXbbCh3/Nk8Ypejf5Kh7m1VfKkkO+HRg6E93 v4My+bik4rLAaLYIsGv9SshOZdmNau2OPOXRbn55FKvzLHytAGhD2cr5wBUhe4xYALx+UD s/KmnMzQ7QkcnlfhWV3x0xtPYz3TeEI= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-561-kqroy2-7MvimJ40WgAf0bg-1; Thu, 04 Sep 2025 06:31:37 -0400 X-MC-Unique: kqroy2-7MvimJ40WgAf0bg-1 X-Mimecast-MFC-AGG-ID: kqroy2-7MvimJ40WgAf0bg_1756981897 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-45b80aecb97so7363365e9.3 for ; Thu, 04 Sep 2025 03:31:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1756981896; x=1757586696; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=iNez6/M9s3PJsme5pRqUUeFXGJSz6E2jhwKDhn5HC94=; b=BOSEOkOOUTVcTKzgjYDii/RPajzOY+2ADAI/fTy+GmXaoVhUVVrcPPeZa+mb/tu0XM uORXUbgSDPRbYDCy0NP2i2u8sTliboYrd4uncvLiUYyZ0XcKQcszWarZO2H8D8AOAfkM z8aAbDN45WNKnCwxt0qGhT0MU7Q2l+RA5lD7zWZuAUf7d0oTaRzkap6RIYSxOmFx+LZM ujtD4a74B5Mq7aPcAHfOH7P8huK7AEqMIza+qG0uhun/iuvKUSn5qjHlSRY7BDmfpyiQ u02m30vUkhPXcmVd2FsguAkj408+SCWGvgum92quan3dfKpABMKHXHju+6znStbbQ1D3 XCOQ== X-Forwarded-Encrypted: i=1; AJvYcCUVOVaK5Sw8ol5uIc46LrVpa+GeiF4VtkO/snWge6MTnAgPg9XTj6ZxTYKt7ZGpqNy0ORxjX5cfcg==@kvack.org X-Gm-Message-State: AOJu0YxDEaGiAw+G+sqmTZjDuXOfFJARWObS4z6HzahQb/b+AATfq2gp t+SsvbLhwBV5q9L09KBvZjA1ez0YJpYeWTRjtVMlxrH4ynUskfKL0U/UVy48GLTfKJqK/gtSCO1 oXDwBw44ocsJIOZDqCNccQ+MZQDoJU91CMb1fT6x3eDC95I4m7IVW X-Gm-Gg: ASbGncudM6srylhVlmNzL5fz3QvaFJetEz6+/pZ0sqnMoEgNy7ucmHzDO7IyBPeCBdW Xs/SOxdUfWOI41GARPcLlIm1lQGDRLreCyxeU3RpXBF5OKcp6UpYvCqbNSAVloObX+4PPQhTvKd 1HkDs8fsl3MFTPPjQORps3kKhk2+gznZJZkGLYA+Wy6OYtXc0HeZhjS0sPyYtxS9Qy/bjxZOJEQ TCLWrdxLuQFgxdqsv/wR66SgXaBw1K/0asV2K2vLJmvUezae+/CXXWsRN0qrlJ2sFIb+VnfTRXl k9XqajeZ7Mm3U4xpwbmJWjALX/srQcCzE2/gLLsKHSKKX0qDH7cjUAfJMRT9tTe5B3o9qWodsYx zFqao+oR7TqX5nUqfqts5bndm8iDkTCCX5zqpG0OjFBWrWCYS3HHwfwiKrJYpEGui X-Received: by 2002:a05:600c:1386:b0:45b:81ad:336 with SMTP id 5b1f17b1804b1-45b855340e4mr168285035e9.16.1756981896476; Thu, 04 Sep 2025 03:31:36 -0700 (PDT) X-Google-Smtp-Source: AGHT+IG3MLtM5QDjEU/zOfZe3S/gDem/oxe78HJp4IABGPJ9GtWj8bc+E5LqhZjiV2Kjt/XWKXc5aQ== X-Received: by 2002:a05:600c:1386:b0:45b:81ad:336 with SMTP id 5b1f17b1804b1-45b855340e4mr168284645e9.16.1756981895992; Thu, 04 Sep 2025 03:31:35 -0700 (PDT) Received: from ?IPV6:2003:d8:2f25:1e00:ce4c:be3:97b3:6587? (p200300d82f251e00ce4c0be397b36587.dip0.t-ipconnect.de. [2003:d8:2f25:1e00:ce4c:be3:97b3:6587]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3d7ac825b88sm14277593f8f.7.2025.09.04.03.31.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Sep 2025 03:31:35 -0700 (PDT) Message-ID: <0ba60468-fc6d-4f07-a9ea-e16b8bcd5575@redhat.com> Date: Thu, 4 Sep 2025 12:31:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: tag kernel stack pages To: Matthew Wilcox Cc: "Vishal Moola (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton References: <20250820202029.1909925-1-vishal.moola@gmail.com> <96148baf-f008-449b-988b-ea4f07d18528@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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: -p9goVbWpLeTOjH5QHOvC2kr9KM33nIik9LU2t3-bBc_1756981897 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: F1A5F80007 X-Stat-Signature: enc1jj379fbf5g4oronb1gu1b41jdzd8 X-Rspam-User: X-HE-Tag: 1756981899-992244 X-HE-Meta: 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 uu/3Mds4 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 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 02.09.25 21:52, Matthew Wilcox wrote: > On Thu, Aug 21, 2025 at 02:44:31PM +0200, David Hildenbrand wrote: >> On 20.08.25 22:20, Vishal Moola (Oracle) wrote: >>> Currently, we have no way to distinguish a kernel stack page from an >>> unidentified page. Being able to track this information can be >>> beneficial for optimizing kernel memory usage (i.e. analyzing >>> fragmentation, location etc.). Knowing a page is being used for a kernel >>> stack gives us more insight about pages that are certainly immovable and >>> important to kernel functionality. >> >> It's a very niche use case. Anything that's not clearly a folio or a special >> movable_ops page is certainly immovable. So we can identify pretty reliable >> what's movable and what's not. >> >> Happy to learn how you would want to use that knowledge to reduce >> fragmentation. :) >> >> So this reads a bit hand-wavy. > > I have a theory that we should always be attempting to do aligned > allocations if we can, falling back to individual allocations if > we can't. This is an attempt to gather some data to inform us whether > that theory is true, and to help us measure whether any effort we > take to improve that situation is effective. > > Eyeballing the output of tools/testing/page-types certainly lends > some credence to this. On x86-64 with its 16KiB stacks and 4KiB > page size, we often see four consecutive pages allocated as type > KernelStack, and as you'd expect only about 25% of the time are they > aligned to a 16KiB boundary. That is, at least 75% of the time they > prevent _two_ order-2 pages from being available. I assume, ideally, you'd also know whether all these stack pages belong to the same thread, not various ones, right? ("context" can matter as well) > > As you say, they're not movable. I'm not sure if it makes sense to > go to the effort of making them movable; it'd require interacting > with the scheduler (to prevent the task we're relocating from > being scheduled), and I don't think the realtime people would be > terribly keen on that idea. So that isn't one of the ideas we > have on the table for improving matters. Yeah, while possible I am also not sure if we always want that. > > Ideas we have been batting around: > > - Have kernel stacks try to do an order-N allocation and vmap() > the result, fall back to current implementation > - Have vmalloc try to do an order-N allocation, fall back down the > orders on failure to allocate > - Change the alloc_bulk implementation to do the order-N allocation > and fall back > > I'm sure other possibilities also exist. > >> staring at [1], we allocate from vmalloc, so I would assume that these will >> be vmalloc-typed pages in the future and we cannot change the type later. >> >> [1] https://kernelnewbies.org/MatthewWilcox/Memdescs > > I see the vmalloc subtype as being a "we don't know any better" type. I guess this could get nasty once we would have metadata assigned to the vmalloc allocations (struct vmdesc). > We could allocate another subtype of type 0 to mean "kernel stacks" > and have it be implicit that kernel stacks are allocated from vmalloc. Yes, that would work. > This would probably require that we have a vmalloc interface that lets us > specify a subtype, which I think is probably something we'd want anyway. vmalloc subtypes don't sound like a bad idea. > > I think it's fine to say "This doesn't add enough value to merge it > upstream". I will note one minor advantage which is that typing these > pages as PGTY_kstack today prevents them from being inadvertently mapped > to userspace (whether by malicious code or innocent bug). Yes, as raised elsewhere, if we can do this consistently today (stack -> PGTY_kstack), fine with me. -- Cheers David / dhildenb