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 E8A29356A23 for ; Tue, 17 Mar 2026 10:09:56 +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=1773742197; cv=none; b=QHsyfMA5ejKJ4aC/tVKCixBhyjwTTWO2Mj5/poLGfhzWcixDt8U6Du4X/mXvYRizI84fEYDxCFycM+G6FkBR0iY52MlHyVeTMmWQepLbkRYFxc5orOWkf4MSo2nYZLPtzEuRbVac3x1OWQfdDThjATo6zq0ZQzsNZS8mQn+JyHc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773742197; c=relaxed/simple; bh=QQlenSLdnpmr2kj2nKKcyLITns2TcK1wgsb6jYePg08=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=mLfxD4MIUHcPjuVjkHIDM/QEwVFjtwdzMqWTok6Z85Wm40Y7tQaw36loSCUZKEY0YqqE/3bcNh+RAl277XNpdzqS1tsBRuidGertvJ44sg7Yz3epJFMbvG6aiENQJMRygvKQx22h4yLv5WhvXucqTOfHL9KfY0a6r+XLQCSEW1U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BXNcEhrp; 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="BXNcEhrp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 08E92C4CEF7; Tue, 17 Mar 2026 10:09:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773742196; bh=QQlenSLdnpmr2kj2nKKcyLITns2TcK1wgsb6jYePg08=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=BXNcEhrphAFIjFkkidWl+xycRjMqjZATxemeThUCTqHMYJFaC+EqDxhOXQGds5ATZ h/iCh3rWcSTRxarrO11MiW24yhkpMMRco3TqOaJe+y1eDwmFPuAt2L6NtlojqSrKTa AsJ+025bq9vmqg0yBYsG3bHP3mpNUeiHr2m0u3l4BRjY5jbOZ569DgsnMiKAkpJpe8 nRYy19NTxsksDdys56uHVEGSF3UNnruzKKMEg8vIab1w1HXg0ZhGpji8F23mGsOA8c pHy2Ipa+qF3KIJ8m5COnOyJ99/hP7Emy17STNrtM49TmpGgM0jxoi8iMFnxpjHN4Qj WdBzs2yX6at+g== Message-ID: Date: Tue, 17 Mar 2026 11:09:51 +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 6/7] mm: list_lru: introduce memcg_list_lru_alloc_folio() To: Johannes Weiner , Andrew Morton Cc: 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> <20260312205321.638053-7-hannes@cmpxchg.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: <20260312205321.638053-7-hannes@cmpxchg.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/12/26 21:51, Johannes Weiner wrote: > memcg_list_lru_alloc() is called every time an object that may end up > on the list_lru is created. It needs to quickly check if the list_lru > heads for the memcg already exist, and allocate them when they don't. > > Doing this with folio objects is tricky: folio_memcg() is not stable > and requires either RCU protection or pinning the cgroup. But it's > desirable to make the existence check lightweight under RCU, and only > pin the memcg when we need to allocate list_lru heads and may block. > > In preparation for switching the THP shrinker to list_lru, add a > helper function for allocating list_lru heads coming from a folio. > > Signed-off-by: Johannes Weiner > --- > include/linux/list_lru.h | 12 ++++++++++++ > mm/list_lru.c | 39 ++++++++++++++++++++++++++++++++++----- > 2 files changed, 46 insertions(+), 5 deletions(-) > > diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h > index 4afc02deb44d..df6bd3c64b06 100644 > --- a/include/linux/list_lru.h > +++ b/include/linux/list_lru.h > @@ -81,6 +81,18 @@ static inline int list_lru_init_memcg_key(struct list_lru *lru, struct shrinker > > int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru, > gfp_t gfp); > + > +#ifdef CONFIG_MEMCG > +int memcg_list_lru_alloc_folio(struct folio *folio, struct list_lru *lru, > + gfp_t gfp); > +#else > +static inline int memcg_list_lru_alloc_folio(struct folio *folio, > + struct list_lru *lru, gfp_t gfp) > +{ > + return 0; > +} > +#endif > + > void memcg_reparent_list_lrus(struct mem_cgroup *memcg, struct mem_cgroup *parent); > > /** > diff --git a/mm/list_lru.c b/mm/list_lru.c > index 779cb26cec84..562b2b1f8c41 100644 > --- a/mm/list_lru.c > +++ b/mm/list_lru.c > @@ -534,17 +534,14 @@ static inline bool memcg_list_lru_allocated(struct mem_cgroup *memcg, > return idx < 0 || xa_load(&lru->xa, idx); > } > > -int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru, > - gfp_t gfp) > +static int __memcg_list_lru_alloc(struct mem_cgroup *memcg, > + struct list_lru *lru, gfp_t gfp) > { > unsigned long flags; > struct list_lru_memcg *mlru = NULL; > struct mem_cgroup *pos, *parent; > XA_STATE(xas, &lru->xa, 0); > > - if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru)) > - return 0; > - > gfp &= GFP_RECLAIM_MASK; > /* > * Because the list_lru can be reparented to the parent cgroup's > @@ -585,6 +582,38 @@ int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru, > > return xas_error(&xas); > } > + > +int memcg_list_lru_alloc(struct mem_cgroup *memcg, struct list_lru *lru, > + gfp_t gfp) > +{ > + if (!list_lru_memcg_aware(lru) || memcg_list_lru_allocated(memcg, lru)) > + return 0; > + return __memcg_list_lru_alloc(memcg, lru, gfp); > +} > + > +int memcg_list_lru_alloc_folio(struct folio *folio, struct list_lru *lru, > + gfp_t gfp) The function reads as if we would be allocating a folio ... folio_memcg_list_lru_alloc() ? Or memcg_list_lru_alloc_for_folio() ? LGTM, with my limited understanding of memcg lifetimes :) Reviewed-by: David Hildenbrand (Arm) -- Cheers, David