From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 E84D526E16A for ; Tue, 18 Feb 2025 16:12:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739895156; cv=none; b=oH/oOcYGDbLqnUNWJ0TGwdnyUel6GYiFjRfBuieyywsLIzkCfC2bs6HH7RgPS+IPLTztnNi6ShBiJWxJgJZP6Rlnxk9fIxtgeYWca6OZkX3hZeqXFwNDY9CJ4xYoMKiNRlntUJqUBb6iBfHqCUViRA2BzVa6zr8QjYA9fQmIOgw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739895156; c=relaxed/simple; bh=bhgPQFSELaI350GW+yyUY2g30cWw1ue+kK9U/gBGJ+k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=VwqpQ8PCLbZKTD0kw7GccWGS9PTvOu/cGnS15p1v9bZJ8HE6A0L+jUA36JuXg7vLbkhHC/7fZl2ZjigjptFAJVnBbA/pTifv+VFNwGeu9Czbz7xuxnjxvaM51G2YZjjacHCyZ8tRThFFzWCRyjcNZppU8xk/M4syPHj7ikfgIJI= 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=hr/ywwtv; arc=none smtp.client-ip=170.10.129.124 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="hr/ywwtv" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739895153; 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=qPrl3VBWVHIaEvfm5FHekwOGQkEzqzqF8ZKou2UTYEw=; b=hr/ywwtv5e4EfBC3b1q/45VtXDwFd8n3TaNQQ4E2pQfO/WNx/c4ov4ZbId2VZAimjq/XnG vkNVh+Iqgz+HgN5KKCF3NMwSNtxDA5PpbOhEubfJG0arRVUWOP/5GI3/S5C/zaPcFooRgX PMtl2dzjW4y4GhgJz3nOLXLw9y6GPGE= 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-653-bG4aQa-wPWO5QYe33EF6Aw-1; Tue, 18 Feb 2025 11:12:32 -0500 X-MC-Unique: bG4aQa-wPWO5QYe33EF6Aw-1 X-Mimecast-MFC-AGG-ID: bG4aQa-wPWO5QYe33EF6Aw_1739895151 Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-43933bdcce0so47351365e9.2 for ; Tue, 18 Feb 2025 08:12:32 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739895151; x=1740499951; 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=qPrl3VBWVHIaEvfm5FHekwOGQkEzqzqF8ZKou2UTYEw=; b=Bg2Qzzf46xEG10tyLeDid7SwrkTk6DcymDhKpcDSNXjAW1q25LrsFzAOEPErjsV+R9 t07FQsPDq/XqKOyowCUyvJuTA/iwQw44nHoEuRADehzLCetX4a5gQ6vKksUPs0juEQ2S yt6I8dzDnnDwwMiOV0K5lRkjAf1b35DmQCXS/cw5D6FunryizaYxGWIcWYuW9bHRlFEt PT+eCbTqDHSKixGhWYznInMap70pZuCC4fMHu473WPH4q+4EXDB4YQunlCmc5EahJs5/ gKdqxRh6iyPcNCX/i/fHeas+gIbSiVJMubIYqcxpL+wOv4tENoOKvHqXpk5v9vpnm5c5 bqgA== X-Forwarded-Encrypted: i=1; AJvYcCXqN7Q31bZvBijJKHoCVWxVjYcnyOlUPAxrGxD+l73Bth42KM1R2dnzLcbtrR5dEfnsIM9xTav1YRfF1NU=@vger.kernel.org X-Gm-Message-State: AOJu0Yzs5/KA7uxiHQ3XS8qipN6M9Qv4mOqVuFAN8JPEZs9ShN2A42dE 5DKwzjuez0MgZSzIiIXxKFCN1NVKbqcx6c7rt8lETWYrzPOviNcCSdC31FxTdwW63DeojA79x0v pwNPvvj6WpEvDPz2iL1Bk4dkZDHUGUWN93MhU0/XTJZkszmiKEfm9EWuiDMAmSw== X-Gm-Gg: ASbGncs7+3n1AX5MqYJT/tAlcMKueWwrEvizep88ddhAKc+rkr4lqCprkKuxYxw010U GN5GzWM/Q0DvAMZHNzwYjfCRxuoMYRvvEyRTaICzcBULU9pLuu+E7JgxmCJtAU+mvDLD60DLYqQ GtrTvMb2rTK4idH/FhwXAxzzsQKqNVVUbd+pOIAW//ZFIfYFikfiMgsqLIEmwc6s4FmnCCTQBT/ xZ4/VGqPFADnHFO4YATSv1Q61V+KT2Qa+QW57JKixvkOd1ofNToMKwKWVbyMUkqyPEeaYBAE7k8 gB5/blt+KtJUki3tkV2supo86TYo3qYs5w== X-Received: by 2002:a05:600c:3ba6:b0:439:91dd:cfaf with SMTP id 5b1f17b1804b1-43999da55damr2421585e9.18.1739895151237; Tue, 18 Feb 2025 08:12:31 -0800 (PST) X-Google-Smtp-Source: AGHT+IH92K++cC6xDJY2j/PMK6R78q23skDZQsnW1aMpOh6cHc3xvEiDq38ZeyklE0eZ+XCX3RGQFw== X-Received: by 2002:a05:600c:3ba6:b0:439:91dd:cfaf with SMTP id 5b1f17b1804b1-43999da55damr2421325e9.18.1739895150812; Tue, 18 Feb 2025 08:12:30 -0800 (PST) Received: from [192.168.3.141] (p5b0c61a2.dip0.t-ipconnect.de. [91.12.97.162]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259fdce7sm15527728f8f.96.2025.02.18.08.12.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Feb 2025 08:12:29 -0800 (PST) Message-ID: Date: Tue, 18 Feb 2025 17:12:27 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 1/8] xarray: add xas_try_split() to split a multi-index entry. To: Zi Yan Cc: linux-mm@kvack.org, Andrew Morton , "Kirill A . Shutemov" , "Matthew Wilcox (Oracle)" , Ryan Roberts , Hugh Dickins , Yang Shi , Miaohe Lin , Kefeng Wang , Yu Zhao , John Hubbard , Baolin Wang , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250211155034.268962-1-ziy@nvidia.com> <20250211155034.268962-2-ziy@nvidia.com> <0bb75517-9418-4145-8aa8-b05373010711@redhat.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >> >> Now, can it happen that xas_try_split() would ever perform a partial split in any way, when invoked from __split_unmapped_folio(), such that we run into the do { } while(); loop and fail with -ENOMEM after already having performed changes -- xas_update(). >> >> Or is that simply impossible? > > Right. It is impossible. xas_try_split() either splits by copying @entry > to all the replacement entries, or is trying to allocate a new xa_node, > which can result in -ENOMEM. These two will not be mixed. > >> >> Maybe it's just the do { } while(); loop in there that is confusing me. (again, no expert) > > Yeah, that the do while loop is confusing. Let me restructure the code > so that the do while loop only runs in the @entry copy case not the > xa_node allocation case. Great! > >> >>> xas_try_split() imposes what kind of split it does and is usually used to >>> split from order N to order N-1: >> >> You mean that old_order -> split_order will in the case of __split_unmapped_folio() always be a difference of 1? > > Yes for !uniform_split case. For uniform_split case (split_huge_page*() uses), > xas_split() is used and all required new xa_node are preallocated by > xas_split_alloc() in __folio_split(). Got it, thanks! -- Cheers, David / dhildenb