From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 8B0AD558218 for ; Tue, 8 Sep 2026 15:07:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788880077; cv=none; b=K7Bw9gLKgaRkqy3c+kgB+himn8/fiSaZZlCT3pytBdu4YmwCqV+vt0nsq+EkUxdRICMBYosBqrKuu8s2X/tiQ+MlkHt2TfEiU1rIBG+lD78kBLs+W4bGjshzdn6EDSs2H44l0E1JtSvEGVwKFga88tuAYwlvifqW5wPNmtDT47M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788880077; c=relaxed/simple; bh=d4Q2zLt3ieSVP12saAart1vpTxsBMp+NxFkPlMaj3yk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qhbTMS/pQInzosnbzro/6sPlBgk/U7u+tvNIFsL2huP9EgI7eTvPmcmvQJFJVyAvb9McKfezjjOpCE+mrmlzVzoZdGbELetL4JgAM701XTtHn465xu2oOoxz/+1jvUoXCXH+pMYh3mniX7z0W1zXqTZDiKkhUTG1HHeUBtI+ruQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE3991F00A3D; Tue, 8 Sep 2026 15:07:36 +0000 (UTC) Message-ID: <60fe39c2-d92f-4bd0-be33-04d702f8f753@kernel.org> Date: Tue, 8 Sep 2026 17:07:28 +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 v3 01/14] mm/zsmalloc: replace PG_private with pointer comparison To: Zi Yan , "Matthew Wilcox (Oracle)" , Andrew Morton , Muchun Song , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Gregory Price , Ying Huang , Alistair Popple , Johannes Weiner , Qi Zheng , Shakeel Butt , Kairui Song Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Minchan Kim , Sergey Senozhatsky References: <20260907-remove-pg_private-v3-0-6ae22f9d9272@nvidia.com> <20260907-remove-pg_private-v3-1-6ae22f9d9272@nvidia.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: <20260907-remove-pg_private-v3-1-6ae22f9d9272@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/8/26 04:56, Zi Yan wrote: > zsmalloc uses PG_private to indicate first zpdesc in a zspage chain. It is > equivalent to check zpdesc == zspage->first_zpdesc. Replace > is_first_zpdesc() with zpdesc == zspage->first_zpdesc in obj_allocated(). > > For get_first_zpdesc(), first_zpdesc is from zspage->first_zpdesc, so > replace is_first_zpdesc() with first_zpdesc->zspage == zspage, the second > requirement of a zspage chain, where all zpdescs point to the same zspage. > > is_first_zpdesc(), is only used in VM_BUG_ON_PAGE(), so performance impact > should be negligible. While at it, change VM_BUG_ON() to > VM_WARN_ON_ONCE_PAGE(). > > It prepares for a future commit that remove PG_private. > > No functional change intended. > > Assisted-by: Claude:claude-opus-4-8 > Assisted-by: Codex:gpt-5 Assied-by: LLM :) > To: Minchan Kim > To: Sergey Senozhatsky > To: Andrew Morton > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Acked-by: Johannes Weiner > Signed-off-by: Zi Yan > --- Nice cleanup, one comment below. Acked-by: David Hildenbrand (Arm) > mm/zpdesc.h | 2 +- > mm/zsmalloc.c | 24 ++++++------------------ > 2 files changed, 7 insertions(+), 19 deletions(-) > > diff --git a/mm/zpdesc.h b/mm/zpdesc.h > index b8258dc78548d..4fd81c2e80769 100644 > --- a/mm/zpdesc.h > +++ b/mm/zpdesc.h > @@ -26,8 +26,8 @@ > * with memcg_data. > * > * Page flags used: > - * * PG_private identifies the first component page. > * * PG_locked is used by page migration code. > + * The first component page has zpdesc->zspage->first_zpdesc == zpdesc > */ > struct zpdesc { > unsigned long flags; > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 825022a7a328f..24526185fd31f 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -290,11 +290,6 @@ struct zs_pool { > atomic_t compaction_in_progress; > }; > > -static inline void zpdesc_set_first(struct zpdesc *zpdesc) > -{ > - SetPagePrivate(zpdesc_page(zpdesc)); > -} > - > static inline void zpdesc_inc_zone_page_state(struct zpdesc *zpdesc) > { > inc_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES); > @@ -476,11 +471,6 @@ static void record_obj(unsigned long handle, unsigned long obj) > WRITE_ONCE(*(unsigned long *)handle, obj); > } > > -static inline bool __maybe_unused is_first_zpdesc(struct zpdesc *zpdesc) > -{ > - return PagePrivate(zpdesc_page(zpdesc)); > -} I would keep this helper, reworking it and moving all comments regarding *how* first detection works in there -static inline bool __maybe_unused is_first_zpdesc(struct zpdesc *zpdesc) +static inline bool __maybe_unused is_first_zpdesc(const struct zpdesc *zpdesc) { - return PagePrivate(zpdesc_page(zpdesc)); + /* Only the first zpdesc has its zspage->first_zpdesc set to itself. */ + return zpdesc == zpdesc->zspage->first_zpdesc; } -- Cheers, David