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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69879C07C79 for ; Mon, 22 Apr 2024 19:31:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AA91A6B0087; Mon, 22 Apr 2024 15:31:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A59016B0088; Mon, 22 Apr 2024 15:31:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8F94F6B0089; Mon, 22 Apr 2024 15:31:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 71FA06B0087 for ; Mon, 22 Apr 2024 15:31:35 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id DC58C160DB7 for ; Mon, 22 Apr 2024 19:31:34 +0000 (UTC) X-FDA: 82038162108.30.EA63F1D Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf25.hostedemail.com (Postfix) with ESMTP id 85662A0013 for ; Mon, 22 Apr 2024 19:31:32 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ExsgPTj8; spf=pass (imf25.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1713814292; 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=nfeRiUr9RWa+jMkA5amGoh/iwJKq4yrGajf3G0hyl8g=; b=1ftDMG2BwGrkDENekk8HfRUybXDUKrNkTiWGOcrDuMXiPIhVNukj2DyXZksbSSQdSxPX/T aEfuv94mIu0U9Ds8gwJ0AE8V/OgUVSSPLCebgRFjhyfd9kl9gAluR2GXCYa0iqFSUPKZbg /YnUCnYjIw8tltpm/AyCP1Uwxi77PKg= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ExsgPTj8; spf=pass (imf25.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1713814292; a=rsa-sha256; cv=none; b=rOaC0KgmaetAsgx9i2sXRTgaEJTNvgfl2nG783RKT4QZ5SQcCyNkJV3ZrS/1kvTS7FAWtP kZv25umrWwMLxHIuD3rJVn/YryVZx4yy1wQqnIS9Ok+pBrxW9DK9ChWVgYdV6smvkxcEYe JLarX5EGiOdFu8LYF5ZwAXGzB4O4mzY= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1713814291; 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=nfeRiUr9RWa+jMkA5amGoh/iwJKq4yrGajf3G0hyl8g=; b=ExsgPTj8ZuUkqyADTzCIuENuNY/KJorYLiwcfgaF/DGMAfEod4ooY/7Ja6z+ikG2f1V8me Q9sVVhK9LdSAy/o0SMIGUS/sQ4QMqjVGOhKZd/dNaE243FS4rjlO8S2Yq/ZEne7PqBfORP SOxG0qkZRjoI7H0FHM7RPcQpYvMbE/U= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-659-ZEoO_kQLMLOsWvoTH0CTJg-1; Mon, 22 Apr 2024 15:31:29 -0400 X-MC-Unique: ZEoO_kQLMLOsWvoTH0CTJg-1 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-34b08e09bc4so1051945f8f.1 for ; Mon, 22 Apr 2024 12:31:29 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1713814289; x=1714419089; h=content-transfer-encoding:in-reply-to:organization:autocrypt:from :content-language: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=nfeRiUr9RWa+jMkA5amGoh/iwJKq4yrGajf3G0hyl8g=; b=E58qaDLepr1KzkkbN/G0BStQN56sey3bcmDza8ndol2AtqOSGLQl/8m37MxqU8Wyiy 7uCTSActVxAwJnoMbnDU9Lq1binJgbiDhh85+D4ApL6W+T+1+tu+mJ8iIskxwGapl9at si+8Q3fAf1sYMeb1fUlEg1uOa6FSvfJ3DCcjKJ+Bk/tBi432A5u6ycAnqOFHYJ203Hr7 AamZPYxFVhzeKyY5FpghrJKdiNEvw3IjQEQjswSSF9DG6rBsUlXIZpMsQcEADnMrq7BZ 3iT8D7NPAqEIGQdWLXuoiEtmy7VY5ZXohAmyp7DEW/YObYOzjKRDjNrWZjiYSPdqtcJP U+/g== X-Gm-Message-State: AOJu0YzZyjk3jzOCXmCp/ZwvdIJsQs10pjViKJUNybW/5AcLz+dUzUdC HvYZGdoYYI9wIxVLdLATt85Mc2bMNn4DBVJmJKGHeK5ffDgrTA92EEKt172lLmlWjBmC6Ht/ise 9R6PiVz4Jd/pOUN8hk9C7IAPxdgRk8+EkOWvd9sQP/R3AF5nC X-Received: by 2002:a05:6000:10c:b0:346:c0f6:8b8 with SMTP id o12-20020a056000010c00b00346c0f608b8mr9026760wrx.12.1713814288737; Mon, 22 Apr 2024 12:31:28 -0700 (PDT) X-Google-Smtp-Source: AGHT+IErrJssZudGpU2It9IqQjWUj9slucUsRnpeHOVjF4pGZ34BGunkw5/JXthgYECez89vO2Z1BA== X-Received: by 2002:a05:6000:10c:b0:346:c0f6:8b8 with SMTP id o12-20020a056000010c00b00346c0f608b8mr9026741wrx.12.1713814288236; Mon, 22 Apr 2024 12:31:28 -0700 (PDT) Received: from ?IPV6:2003:cb:c739:600:d2fb:3a8a:9944:7910? (p200300cbc7390600d2fb3a8a99447910.dip0.t-ipconnect.de. [2003:cb:c739:600:d2fb:3a8a:9944:7910]) by smtp.gmail.com with ESMTPSA id je12-20020a05600c1f8c00b004183edc31adsm21293294wmb.44.2024.04.22.12.31.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Apr 2024 12:31:27 -0700 (PDT) Message-ID: Date: Mon, 22 Apr 2024 21:31:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/huge_memory: improve split_huge_page_to_list_to_order() return value documentation To: John Hubbard , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Zi Yan , Matthew Wilcox , Andrew Morton References: <20240418151834.216557-1-david@redhat.com> <18faa967-4fbc-4694-a7f7-02c3887ee6f3@nvidia.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: <18faa967-4fbc-4694-a7f7-02c3887ee6f3@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: ok3cjnw9rgyt1a1t5picy6zj76nq64mg X-Rspamd-Queue-Id: 85662A0013 X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1713814292-38718 X-HE-Meta: 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 suKkp6u+ 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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 19.04.24 02:15, John Hubbard wrote: > On 4/18/24 8:18 AM, David Hildenbrand wrote: >> The documentation is wrong and relying on it almost resulted in BUGs >> in new callers: we return -EAGAIN on unexpected folio references, not >> -EBUSY. >> >> Let's fix that and also document which other return values we can >> currently see and why they could happen. >> >> Cc: John Hubbard >> Cc: Zi Yan >> Cc: Matthew Wilcox >> Cc: Andrew Morton >> Signed-off-by: David Hildenbrand >> --- >> mm/huge_memory.c | 13 ++++++++++--- >> 1 file changed, 10 insertions(+), 3 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index ee12726291f1b..824eff9211db8 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -2956,7 +2956,7 @@ bool can_split_folio(struct folio *folio, int *pextra_pins) >> * >> * 3) The folio must not be pinned. Any unexpected folio references, including >> * GUP pins, will result in the folio not getting split; instead, the caller >> - * will receive an -EBUSY. >> + * will receive an -EAGAIN. >> * >> * 4) @new_order > 1, usually. Splitting to order-1 anonymous folios is not >> * supported for non-file-backed folios, because folio->_deferred_list, which >> @@ -2975,8 +2975,15 @@ bool can_split_folio(struct folio *folio, int *pextra_pins) > > As an aside, the use of unconditional local_irq_disable() / local_irq_enable() > calls in this routine almost makes me believe that we should have: > > 5) Local IRQs should be enabled. Because this routine may enable them. > > ...but I can't imagine a way to end up calling this with interrupts > disabled, so it seems like documentation overkill. Just thought I'd mention > it, though. Yes, I think there might be more issues lurking with disabled interrupts. anon_vma_lock_write() and i_mmap_lock_read() might even sleep ... so we must not be in any atomic context. that's why relevant page table walkers drop the PTL. > > >> * >> * Returns 0 if the huge page was split successfully. >> * >> - * Returns -EBUSY if @page's folio is pinned, or if the anon_vma disappeared >> - * from under us. >> + * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP). > > ...or if the folio was removed from the page cache before this routine > got a chance to lock it, right? (See the "fail:" path.) Right, that is sneaky. Let me extend to cover that case as well. diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 824eff9211db8..a7406267323ed 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2975,7 +2975,8 @@ bool can_split_folio(struct folio *folio, int *pextra_pins) * * Returns 0 if the huge page was split successfully. * - * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP). + * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP) or if + * the folio was concurrently removed from the page cache. * * Returns -EBUSY when trying to split the huge zeropage, if the folio is * under writeback, if fs-specific folio metadata cannot currently be Naive me would assume that this happens rarely ... but not an expert :) > >> + * >> + * Returns -EBUSY when trying to split the huge zeropage, if the folio is >> + * under writeback, if fs-specific folio metadata cannot currently be >> + * released, or if some unexpected race happened (e.g., anon VMA disappeared, >> + * truncation). >> + * >> + * Returns -EINVAL when trying to split to an order that is incompatible >> + * with the folio. Splitting to order 0 is compatible with all folios. >> */ >> int split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >> unsigned int new_order) > > Otherwise, looks good. Thanks! -- Cheers, David / dhildenb