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 B924D1C3C11 for ; Mon, 20 Oct 2025 19:26:49 +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=1760988411; cv=none; b=BPxx02DWIKbCNGnvTX6rwKoUX2TaMLMQQi9ROGb96jSkJGwV0nQsGrjL6AzorFCPg7tp6gKdyXt80f9A2+B594QTZYAr2PhgmdEgaHWr04cmt+PTiLNjj7IHOtXjcqp8cGVUSVlD/OpDVuhpt5esjA5Tvk/JK9O6D6DngGvMq38= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760988411; c=relaxed/simple; bh=vxL4eTLs7yhxNYDXcAIfQ+nyLiInBV6G9WxtlOGz4q8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fJSscCqmOz4Bp75CxYEWaI1egrjii2NdwZaDUmW1kZ2ohBYic6u8Hp0t2l/nMmacQo0g7pJ7ndKjOokqyyNG3sv1MGpgxR13cQnR+QwL4FaMzz9M0hbh1Bor5A0dTdELZ6IhyHWMLeowuNJTjCCbqX6evN8YRO1XpSkwPpjUpDY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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=NQv+Sa6J; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine 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="NQv+Sa6J" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1760988408; 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=UTXB7/q8p4TNL9vNa5DPOotMkbp1a/zM+v7YOiHTFsA=; b=NQv+Sa6JQvu8B8wBvZGp75fqP2zfbw/izR09vrM8hYnI8B9sIBllSbN4bwo6pwcSOQ+ndC 4mdWJstn4zCtjYtVWF320Vawl3/vRSm+0RylL2X8pVESX9hB3JkBf9hXqyMsaLk1RpEg3h WWyPG8988tm8V8INwuQgD7m3MtRmZT0= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-654-IQaNfCdiP5CxvQS3EQuChA-1; Mon, 20 Oct 2025 15:26:46 -0400 X-MC-Unique: IQaNfCdiP5CxvQS3EQuChA-1 X-Mimecast-MFC-AGG-ID: IQaNfCdiP5CxvQS3EQuChA_1760988405 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-46b303f6c9cso54764755e9.2 for ; Mon, 20 Oct 2025 12:26:46 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1760988405; x=1761593205; 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=UTXB7/q8p4TNL9vNa5DPOotMkbp1a/zM+v7YOiHTFsA=; b=s9AXDeUKuM5J3oDkyjJCO/HOtJ7rlkeHv2Gu5iRTNCndfA2lxYVOtRrbe4UCY3UDX/ 1XkjyYExskd4hRjNKYO1tF5TfM+04WawHIRVZH8GzQhzZdPG6cgoxqPqsNWvXlA99zjw QxihI5BDKpW3EPszvqIQagfXGf7VaVSWVpgv6mHdZKZtHeRnu6m9mm752BDSBpm+figl xo8z+/fYOcSiBSPHL/uR5qWsYQq2XP54PffeZ+tf2W0wyPqPJ2udGWdHK60eexCi7ooQ wSPYHZxrImMjH2rb/i4BCxyEvgXUYyZfMdUOjdp8cZ1vQEFqV/GADIAZmRmjOvxTnb7+ avTw== X-Forwarded-Encrypted: i=1; AJvYcCXfrNsMtWHsj0aYGSXCz6SY9aaY3Rz+JSf0KLwcZGKbNL6zqmO28b6Rx8ckefxgUpuIgKr+eza0I095dAQ=@vger.kernel.org X-Gm-Message-State: AOJu0YwZt/ht7HwC1hYXFVp6CiSaGj3vCllPfVpIGPuDC8sWktZWyw+7 3qyBi55dk64XSG6ZW9rymxd8xJINNzACDNauO/QgG4sBSvBB6K2OC/U7klWDpBTHSVfDaEe/sj3 1yrlUqNbGlwq69qmdrEUus1g5MAFD+DPuDkti0v8CgPcPUAnZ9lGD3REFy+4dQluVoQ== X-Gm-Gg: ASbGnctTXH6WIQ6hk8esOzRjOyPg1QiVK8QA3NXzdRvSHMHiM/dPafMOs8sa65ws5OV +n/OUzZdbXrsJBz/RcNFk2dNblJGw9FRdC77VeZ+5vUGnMP7Dxv6RNcSk6iplZlPdXxFJ/neZwX kkqeSL0ap1LKvc55sH+e7H3sVr291ID2+T2fTym9dB7J1hd36Dg7SrqUDwF75sANu6BNi/OtgfJ Dv0Gl7N2QjYWU2MCtfj7eKwLcTIjWKVHnBbrQnvI7wz0yQBOtP/Q8Wih/9/4dFrnb/QjmgTyjX5 kfEfSTH9EZ3NIm9E080fCsge+XnhdZhnVZQMsFaAyaMHWr7udzMuo2eXwt6idRSOGcyLvhC7iPg IbS1tt5z7MMz6pyMe0oAQc9XZU6oeUlXDnHzicbR34nJZhiFf9Qg+nNFT4K4yn/H1v9I+GVQtcO koLUs/g/d1TvCVjqqTbeq5Jwya5jw= X-Received: by 2002:a05:600c:8185:b0:471:14e7:e988 with SMTP id 5b1f17b1804b1-47117925d0emr107430325e9.35.1760988404970; Mon, 20 Oct 2025 12:26:44 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGfhRTNhNg7YWVfxTym0dxgSdzchCcacq4Q770pmVWsBNDJLEfc+4CUgQteSBDZjY1EjbrX9Q== X-Received: by 2002:a05:600c:8185:b0:471:14e7:e988 with SMTP id 5b1f17b1804b1-47117925d0emr107430195e9.35.1760988404582; Mon, 20 Oct 2025 12:26:44 -0700 (PDT) Received: from ?IPV6:2003:d8:2f0c:c200:fa4a:c4ff:1b32:21ce? (p200300d82f0cc200fa4ac4ff1b3221ce.dip0.t-ipconnect.de. [2003:d8:2f0c:c200:fa4a:c4ff:1b32:21ce]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47494ab11bbsm2352275e9.1.2025.10.20.12.26.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Oct 2025 12:26:44 -0700 (PDT) Message-ID: <7e43294a-03d5-42e5-bec2-5fbcfab97b69@redhat.com> Date: Mon, 20 Oct 2025 21:26:42 +0200 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] mm/page_isolation: clarify FIXME around shrink_slab() in memory hotplug To: Manish Kumar , akpm@linux-foundation.org Cc: vbabka@suse.cz, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20251015175041.40408-1-manish1588@gmail.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 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: <20251015175041.40408-1-manish1588@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 15.10.25 19:50, Manish Kumar wrote: > The existing FIXME comment notes that memory hotplug doesn't invoke > shrink_slab() directly. This patch adds context explaining that this is > an intentional design choice to avoid recursion or deadlocks in the > memory reclaim path, as slab shrinking is handled by vmscan. > > Signed-off-by: Manish Kumar > --- > mm/page_isolation.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index b2fc5266e3d2..2ca20c3f0a97 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -176,10 +176,16 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ > > /* > * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself. > - * We just check MOVABLE pages. > + * > + * This is an intentional limitation: invoking shrink_slab() from a > + * hotplug path can cause reclaim recursion or deadlock if the normal > + * memory reclaim (vmscan) path is already active. Slab shrinking is > + * handled by the vmscan reclaim code under normal operation, so hotplug > + * avoids direct calls into shrink_slab() to prevent reentrancy issues. This is the first time I hear about this reentrance issue. How did you come up with this explanation? -- Cheers David / dhildenb