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 38A1A2EC08C for ; Thu, 19 Mar 2026 07:21:25 +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=1773904886; cv=none; b=SKoJTNaDXNc04Ek3Fme2WtnToCON2IA89pgKVaRWmjuBimzwpC0GGYElCg1+UkrRp8ATNL/ziB9uqinzYm0QGoOUqFlCXK5kp4lxphZSPC5CNdNat2wS68i3P9JoYBCtr+6XXmuYIhQyZlSQUCX7NUCEtlzujHzHVzPNxtoRU9Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773904886; c=relaxed/simple; bh=CspEV/eL2jUsFjVlynNQZqKA/uixA05pxZrqR2Qsnx8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CGsUJKeH6tJDVFVug+j8l/JsY63SfpZPgMj05Krq0bEVMbEXT7k6xYa8ZLaCMTvBujPBmXJlYYSQg2V6mu7dAVNJehXY5d4IZwzBawtQ6ZLjNdcr6vQsFr12grGjUlzh4VZGia6h1jDmBjTS0qi8nfsvElOxmOXe/3xuU6Bd91o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AV6ddI55; 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="AV6ddI55" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E71AC19424; Thu, 19 Mar 2026 07:21:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773904885; bh=CspEV/eL2jUsFjVlynNQZqKA/uixA05pxZrqR2Qsnx8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=AV6ddI55Ndkjzzz3wu3kEgTrfY/Ql9eyIC8/LV0ef31ZjJaEEXTRmvTxeDBs3RC63 c+i7DjJ8JvUNYIaj+sbA9CQJVXAzgOOVq6hYoMD9YS1Eu2yjBgcxdaGQMn6rvtNOn7 iedvX0w7hROERMiK7QDZciTMlJYtxDtA2tKVmDaFe/lyODJYTx5jHEq4M2cVRYGQtQ ZGLe/Fnqpq8Yq3sSfWf9C+vUXUnicrt3Co6cXNpsxxtaVTPQgtHmUUGhPm5vL/w4+s t3rRHYWXZ1i0a21ygfU4tnchQyJmIXmGbRZthvQvo+OhD6wBj5Uu2m6N4rQEo2Zxsi exeS7+rLeE9lQ== Message-ID: Date: Thu, 19 Mar 2026 08:21:21 +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 v2 7/7] mm: switch deferred split shrinker to list_lru To: Johannes Weiner Cc: Andrew Morton , Shakeel Butt , Yosry Ahmed , Zi Yan , "Liam R. Howlett" , Usama Arif , Kiryl Shutsemau , Dave Chinner , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260312205321.638053-1-hannes@cmpxchg.org> <20260312205321.638053-8-hannes@cmpxchg.org> <61d86249-cd89-4e99-99d8-ab7c72e95f34@kernel.org> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit >> >> So, in all anon alloc paths, we essentialy have >> >> 1) vma_alloc_folio / __folio_alloc (khugepaged being odd) >> 2) mem_cgroup_charge / mem_cgroup_swapin_charge_folio >> 3) memcg_list_lru_alloc_folio >> >> I wonder if we could do better in most cases and have something like a >> >> vma_alloc_anon_folio() >> >> That wraps the vma_alloc_folio() + memcg_list_lru_alloc_folio(), but >> still leaves the charging to the caller? > > Hm, but it's the charging that figures out the memcg and sets > folio_memcg() :( Oh ... right. I guess we would then have to do all 3 things at the same time, which makes the helper a bit more involved. I'll note that collapse_file() also calls alloc_charge_folio(), but not for allocating an anonymous folio that would have to be placed on the deferred split queue. > >> The would at least combine 1) and 3) in a single API. (except for the >> odd cases without a VMA). >> >> I guess we would want to skip the memcg_list_lru_alloc_folio() for >> order-0 folios, correct? > > Yeah, we don't use the queue for < order-1. In deferred_split_folio(): > > /* > * Order 1 folios have no space for a deferred list, but we also > * won't waste much memory by not adding them to the deferred list. > */ > if (folio_order(folio) <= 1) > return; > >>> @@ -3802,33 +3706,28 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n >>> struct folio *new_folio, *next; >>> int old_order = folio_order(folio); >>> int ret = 0; >>> - struct deferred_split *ds_queue; >>> + struct list_lru_one *l; >>> >>> VM_WARN_ON_ONCE(!mapping && end); >>> /* Prevent deferred_split_scan() touching ->_refcount */ >>> - ds_queue = folio_split_queue_lock(folio); >>> + rcu_read_lock(); >> >> The RCU lock is for the folio_memcg(), right? >> >> I recall I raised in the past that some get/put-like logic (that wraps >> the rcu_read_lock() + folio_memcg()) might make this a lot easier to get. >> >> >> memcg = folio_memcg_lookup(folio) >> >> ... do stuff >> >> folio_memcg_putback(folio, memcg); >> >> Or sth like that. >> >> >> Alternativey, you could have some helpers that do the >> list_lru_lock+unlock etc. >> >> folio_memcg_list_lru_lock() >> ... >> folio_memcg_list_ru_unlock(l); >> >> Just some thoughts as inspiration :) > > I remember you raising this in the objcg + reparenting patches. There > are a few more instances of > > rcu_read_lock() > foo = folio_memcg() > ... > rcu_read_unlock() > > in other parts of the code not touched by these patches here, so the > first pattern is a more universal encapsulation. > > Let me look into this. Would you be okay with a follow-up that covers > the others as well? Of course :) If list_lru lock helpers would be the right thing to do, it might be better placed in this series. -- Cheers, David