From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 69415195FEC for ; Fri, 9 Aug 2024 13:47:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723211277; cv=none; b=Ldf2q7XxSxpXHD8W0KlN7MMYgtLa4WsoRyvKEgZnxnvwamsQNAeeREd+r6xkbqryD4lmBJfYB+ATf86u50YX2faPpXdRyS97ppRnx7aH8fLGKKaqdXtwnYvMI5H8YImJjghHl69l0F+Q0YjK3ybLCQ5cyDFk0TzFFHg/ggtKjAA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723211277; c=relaxed/simple; bh=h/gETMxwSX7PKWGfoK6CtdX0CU+AONkas3R8CWNCc4w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LAg+YdYl02bO1OSeGwW6tKrfNINdnXaXAnM6+rLO68dzCdB96kfx/pD1DvjX1g253LTFUPUeQVnmwXfsO6PRNDO1VhbFJgN/M2yTvvd8ebuoPBQH4yRmCLMcLCYWay1KgMVLJ+ITGfbnai+jJDWZG7/G1ZjxWAKs3diEJFbq9Ac= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=UT81Uh87; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UT81Uh87" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1723211274; 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=abAgUi1+Zy9/7Tnhw4Fiy6iRsAPB01YF1mBbZxXtcPw=; b=UT81Uh87wSmwLbjvzPL9jVCgRfIgVXMYw0Suivl64Rjuu+aSXvN5mwPp4k7zHONFO1/6Ly eKHnK/JLAZyOY3wpE8QYTeYBP0NdDmeoAoOfE05p19X1G8jy3t8VOxxdiH/Owscp6LbW9s tw3sJZ5spZgBuimNPD1g15jeXDpMLE4= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-564-dSUnlNvWMFiGoozeK3bZxw-1; Fri, 09 Aug 2024 09:47:53 -0400 X-MC-Unique: dSUnlNvWMFiGoozeK3bZxw-1 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-428076fef5dso14742165e9.2 for ; Fri, 09 Aug 2024 06:47:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723211272; x=1723816072; h=content-transfer-encoding:in-reply-to:organization: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=abAgUi1+Zy9/7Tnhw4Fiy6iRsAPB01YF1mBbZxXtcPw=; b=BIct7F1QwLTXkFtLoEMKhwJBRg2mSoWx3ct2bNnSfClCpViYzXoJgyv9YoVeLK3h7N eLjQJ8rlsoiq6p/TihXRu4u2S1O65ed8O99euvkhdQn+F4wEmO/NOVIPJR9XiMhJq1oq NxcRCxiBvk2B76LdqP3LFD98fMD4b+3dnLLHUUUBj7YDxPC35GAXUvMapSm9XZOwCAOz EdZjwcHINUJvJas8xtVScEghLZJBPXNn5NnYMJz9yYtwlsDHQAOFwYA9jyF9YGPivRtP e56u85Xo/8M4v870PnXM74yzgR0Irbgt0WGrzkWpzHAwJ2aG+r5svxLlvkXuE3SwGaWv 0TPQ== X-Forwarded-Encrypted: i=1; AJvYcCWxCXY79gHaaEyw03/xtL+7mY2c9IQxzzw9RNUJzgx8pcnHvnGcQqVOSSZVZeRKqi0wCjRyE2J9iBvll3mrrxiUtEZnWLJvFxNR96dICwAV X-Gm-Message-State: AOJu0YyT8rC13PkYSfIQ5r1Zvdhz3k4bPqdTijUojtfyY0hNSEiA0Sjy jPe31ZVbWE0yZ0RRazmDzeYJKTvQeM1XWZ+46IVPajXwnaPRCmLN7t94FcBrtWpcDjVCQNJRB7B y7nl2gb/cxXjLifkakRdrnm1YLFC8ZY/ukpJezm5stv8CTY+srE7UrbfO8D6mdM+mMw== X-Received: by 2002:a05:600c:81e:b0:426:6ed2:6130 with SMTP id 5b1f17b1804b1-429c3a22f76mr10113355e9.14.1723211271806; Fri, 09 Aug 2024 06:47:51 -0700 (PDT) X-Google-Smtp-Source: AGHT+IH9qBwJZyeDlqvfoQ6FAb16ltqAXPnmsE5wmIP3HkLigyWZbF2pZDcU9Kn8974AQAtPb2jfSA== X-Received: by 2002:a05:600c:81e:b0:426:6ed2:6130 with SMTP id 5b1f17b1804b1-429c3a22f76mr10113115e9.14.1723211271304; Fri, 09 Aug 2024 06:47:51 -0700 (PDT) Received: from ?IPV6:2003:d8:2f09:3f00:d228:bd67:7baa:d604? (p200300d82f093f00d228bd677baad604.dip0.t-ipconnect.de. [2003:d8:2f09:3f00:d228:bd67:7baa:d604]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-429059713c4sm132070245e9.12.2024.08.09.06.47.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 Aug 2024 06:47:50 -0700 (PDT) Message-ID: <761ba58e-9d6f-4a14-a513-dcc098c2aa94@redhat.com> Date: Fri, 9 Aug 2024 15:47:49 +0200 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: Retry migration earlier upon refcount mismatch To: Dev Jain , akpm@linux-foundation.org, shuah@kernel.org, willy@infradead.org Cc: ryan.roberts@arm.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, cl@gentwo.org, vbabka@suse.cz, mhocko@suse.com, apopple@nvidia.com, osalvador@suse.de, baolin.wang@linux.alibaba.com, dave.hansen@linux.intel.com, will@kernel.org, baohua@kernel.org, ioworker0@gmail.com, gshan@redhat.com, mark.rutland@arm.com, kirill.shutemov@linux.intel.com, hughd@google.com, aneesh.kumar@kernel.org, yang@os.amperecomputing.com, peterx@redhat.com, broonie@kernel.org, mgorman@techsingularity.net, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20240809103129.365029-1-dev.jain@arm.com> <20240809103129.365029-2-dev.jain@arm.com> From: David Hildenbrand Content-Language: en-US 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: <20240809103129.365029-2-dev.jain@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 09.08.24 12:31, Dev Jain wrote: > As already being done in __migrate_folio(), wherein we backoff if the > folio refcount is wrong, make this check during the unmapping phase, upon > the failure of which, the original state of the PTEs will be restored and > the folio lock will be dropped via migrate_folio_undo_src(), any racing > thread will make progress and migration will be retried. > > Signed-off-by: Dev Jain > --- > mm/migrate.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/migrate.c b/mm/migrate.c > index e7296c0fb5d5..477acf996951 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1250,6 +1250,15 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, > } > > if (!folio_mapped(src)) { > + /* > + * Someone may have changed the refcount and maybe sleeping > + * on the folio lock. In case of refcount mismatch, bail out, > + * let the system make progress and retry. > + */ > + struct address_space *mapping = folio_mapping(src); > + > + if (folio_ref_count(src) != folio_expected_refs(mapping, src)) > + goto out; This really seems to be the latest point where we can "easily" back off and unlock the source folio -- in this function :) I wonder if we should be smarter in the migrate_pages_batch() loop when we start the actual migrations via migrate_folio_move(): if we detect that a folio has unexpected references *and* it has waiters (PG_waiters), back off then and retry the folio later. If it only has unexpected references, just keep retrying: no waiters -> nobody is waiting for the lock to make progress. For example, when migrate_folio_move() fails with -EAGAIN, check if there are waiters (PG_waiter?) and undo+unlock to try again later. But I'm not really a migration expert, so only my 2 cents :) > __migrate_folio_record(dst, old_page_state, anon_vma); > return MIGRATEPAGE_UNMAP; > } -- Cheers, David / dhildenb