From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C10FB37882E for ; Thu, 23 Apr 2026 10:27:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776940063; cv=none; b=LSNQjniurMOmC6aZ836/CHw0YBYarB6ae7+YpEBpMF40tgUU2CgqEqpAeCsWBXJcWYiQ2aSyFbw0DezI51H3WKkDiBBUfpEDXbGhzIIw1sk1CBvUiS+3iTX5cLxtqzExCunl9yOXkFwpCWDnYsAqCmKIZVPwR4enRPpmcV5fWiw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776940063; c=relaxed/simple; bh=ohdrzIDtFsxHqFS1uvIA5YEDv/bmIvcy1gYpoCoGLJs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=j1qnFfmM85HRHeNOB41TGAcLP08ulywrPgO8tPMUDZKs7ZrPw5a1Qf6LlzUQOxVDytLtXey9Tpqzv3LKRIc3mVdhdSm+gM0CjSm64cwsvFbaDCAxIuAKXSfLZ5dyX2Sn2Z5QiFszx9gU0g18/OsNdkoLSRgA83ZoT/qvL70Nbrs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Ok0FWBV9; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Ok0FWBV9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49A32C2BCB2; Thu, 23 Apr 2026 10:27:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776940063; bh=ohdrzIDtFsxHqFS1uvIA5YEDv/bmIvcy1gYpoCoGLJs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ok0FWBV9PjaTvb9k3tr/bDRO6Bnnsc5r+cgS9c9qb/7vQfS0+dSOy9Rhhpma670eK PX9YCMfDqd4gmFY6VQato7wSoq7iE1xqskFmOMog+FRyLSOY+49eUis37C35malsu/ 9B9ClLYJQTB+0Rk7cmDKNvPeivYtFZP5C0dLcF20QRwTP1x+v9OTW1C1K1CpmJgm3X MROFWVPtcda7rBtLde4TYsImG789mMEZ1xNqs60HHc+UyxIWEDbrS/8wbOdi25muTv F6w1qd/TUuT1/vyNDIoSTR77NjQY194gE6mQFJ+qXhwK35pxVoty+bROtnfsoq6DB8 2yJwECD0NCVoQ== Message-ID: <76191a17-18bf-4e9b-9ab5-dc9a48abfabb@kernel.org> Date: Thu, 23 Apr 2026 12:27:36 +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 v2 1/5] mm: Introduce zone_appears_fragmented() To: Matthew Brost , intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: =?UTF-8?Q?Thomas_Hellstr=C3=B6m?= , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Johannes Weiner , Michal Hocko References: <20260423055656.1696379-1-matthew.brost@intel.com> <20260423055656.1696379-2-matthew.brost@intel.com> 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: <20260423055656.1696379-2-matthew.brost@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 4/23/26 07:56, Matthew Brost wrote: > Introduce zone_appears_fragmented() as a lightweight helper to allow > subsystems to make coarse decisions about reclaim behavior in the > presence of likely fragmentation. > > The helper implements a simple heuristic: if the number of free pages > in a zone exceeds twice the high watermark, the zone is considered to > have ample free memory and allocation failures are more likely due to > fragmentation than overall memory pressure. > > This is intentionally imprecise and is not meant to replace the core > MM compaction or fragmentation accounting logic. Instead, it provides > a cheap signal for callers (e.g., shrinkers) that wish to avoid > overly aggressive reclaim when sufficient free memory exists but > high-order allocations may still fail. > > No functional changes; this is a preparatory helper for future users. > > Cc: Thomas Hellström > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Lorenzo Stoakes > Cc: "Liam R. Howlett" > Cc: Vlastimil Babka > Cc: Mike Rapoport > Cc: Suren Baghdasaryan > Cc: Michal Hocko > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Matthew Brost > --- > include/linux/vmstat.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > index 3c9c266cf782..568d9f4f1a1f 100644 > --- a/include/linux/vmstat.h > +++ b/include/linux/vmstat.h > @@ -483,6 +483,19 @@ static inline const char *zone_stat_name(enum zone_stat_item item) > return vmstat_text[item]; > } > > +static inline bool zone_appears_fragmented(struct zone *zone) > +{ "zone_likely_fragmented" or "zone_maybe_fragmented" might be clearer, depending on the actual semantics. > + /* > + * Simple heuristic: if the number of free pages is more than twice the > + * high watermark, this strongly suggests that the zone is heavily > + * fragmented when called from a shrinker. > + */ I'll cc some more people. But the "when called from a shrinker" bit is concerning. Are there additional semantics that should be expressed in the function name, for example? Something that implies that this function only gives you a reasonable answer in a certain context. -- Cheers, David