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 230C4CD6E64 for ; Wed, 3 Jun 2026 08:05:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 82F4D6B009B; Wed, 3 Jun 2026 04:05:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 80C436B009D; Wed, 3 Jun 2026 04:05:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 71CE16B009E; Wed, 3 Jun 2026 04:05:26 -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 658BF6B009B for ; Wed, 3 Jun 2026 04:05:26 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 322B71C125F for ; Wed, 3 Jun 2026 08:05:26 +0000 (UTC) X-FDA: 84837866652.20.90ED531 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf04.hostedemail.com (Postfix) with ESMTP id 727F840003 for ; Wed, 3 Jun 2026 08:05:24 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="fmi/kQoc"; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780473924; 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=0dQKg3fvoQXUdTatlK6PcboFOhBDiwUnlDV/Gb+Sv7w=; b=XMwlZKEYyAD7y8nVyTxspwKwpFqQIcpS45eVhwGMXC/rm4FYr6q4LV2KKsiNPgbC0zbkrm 0UnmjEJwPHTJOqqlvFZlE7CdKTmi8mSHn9ta8KHCUswx9g6ZbN6EgM+dHwU7tZeelOqynn trHJmrOHZlFwsJJEtDb0ZzQK98S/XKc= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="fmi/kQoc"; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780473924; b=jFoPiff3pnNvR5v55ORHeqCiX/pXTezohceojjARJkbUFhvglirn7zgcS1ArAjMM0LEzRg mpthq52XyrK/yOdFdif4lBlrS7YMm8aT4uSDCM1bpjIo6omPVDd5vkc3kjJ2YSsOjiqpe8 lIM3bybrQap4MXxkUJhF0LIdskTpD9E= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id D575460222; Wed, 3 Jun 2026 08:05:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 281721F00893; Wed, 3 Jun 2026 08:05:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780473923; bh=0dQKg3fvoQXUdTatlK6PcboFOhBDiwUnlDV/Gb+Sv7w=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fmi/kQocICzf2H+zcJHdlBHGwo0Qp9QRK3CjEUT2veesOjS3zCAuHCn+NmJjmPt98 nrsO6B0z1IC672L4/t4Y1ey2578h8UEmrDA8joZieEPy7fS1UbhSDqu8FlN+akaPrF VuQ2Z+PwbFeKKC3UMyalzcXtdRk973pNHZWd8UwSIEGGBND/r6oU4514YT5e0poV37 XdOn8AG5KBM3xUX/CS+NuDl7Emmia3jLYZYd+Kwr14ZFaWnmp+PLUqIBnD8k9ZLzEn 5kSOn3RSVLUcrRg1h7Q7Yf6hkTi2cMBrG3M73fFzhHxOhGC6UhoIIXhM14OdBlibqS hLe3VM63EsOyA== Message-ID: <46bb9d9e-03f0-4e26-9ac9-1cdc5ba9bf4d@kernel.org> Date: Wed, 3 Jun 2026 10:05:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support To: Lance Yang , Nico Pache Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com References: <20260522150009.121603-12-npache@redhat.com> <20260531071845.10875-1-lance.yang@linux.dev> <185f5699-3797-4300-8c54-bb99fc2a45e0@linux.dev> 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: <185f5699-3797-4300-8c54-bb99fc2a45e0@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 727F840003 X-Stat-Signature: bwu5p9hy9fczrkpkd6jjycw9rq1wwrgs X-Rspam-User: X-HE-Tag: 1780473924-555398 X-HE-Meta: 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 F/QvyLpk OoOqhBPmId4OhLocfHmf/8r/92FZalIQD2UhxjYI9iVWVTsym98lc/SwHecC6HV82XgbXXb+4HUEhbk5dLNVQVhE7PcPW9QQSfQ2j2lJY3IhK+m7ATWoeO+5AFrnn0CNwxTmzzjTAAW0XC8oz3QEHggMehyZdsX8VCXcV4C9LGLmn/FRI9TdIpFvOJnJ042+UZRtosOrdIVsbzABcQxi0CXYCbdS3QSofqKeoUt9ozVRKgfvaIny4wLYVD9hiNsJ6Vy1Bg0YqLQxF1Y4mvU9GIZGNNlRUu+BgxXyxw8sFFuzyMTlzZTAp9wZTk7TvnYKofrgMYZcrSyjlcLyDep01MUyFHpigQodqiKnB Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/2/26 17:44, Lance Yang wrote: > > > On 2026/6/2 18:58, Nico Pache wrote: >> On Sun, May 31, 2026 at 1:19 AM Lance Yang wrote: >>> >>> >>> [...] >>> >>> Hmm ... don't we lose the allocation-failure result here? >>> >>> Previously collapse_scan_pmd() propagated SCAN_ALLOC_HUGE_PAGE_FAIL from >>> collapse_huge_page(), so khugepaged would call khugepaged_alloc_sleep() >>> in khugepaged_do_scan(). >>> >>> Now if allocation fails and nr_collapsed stays 0, we just return >>> SCAN_FAIL. So we won't back off via khugepaged_alloc_sleep() anymore? >> >> Ok I did the error propagation! I think I handled both of these cases >> you brought up pretty easily. > > Thanks. > >> However I don't know what to do in the following case: We successfully >> collapsed some portion of the PMD, but during that process, we also >> hit an allocation failure. Is it best to back off entirely? or can we >> treat some forward progress as a sign we can continue trying collapses >> without sleeping. >> >> Basically, do we prioritize SCAN_ALLOC_HUGE_PAGE_FAIL or the >> successful collapses as the returned value? > > Thinking out loud, forward progress should win here, the allocation > failure only matter if we made no progress at all? Agreed, in the first approach, forward progress makes sense. -- Cheers, David