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([2001:1a48:8:903:1ed6:4f73:ce38:f9d4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4854b66e3f8sm30497515e9.14.2026.03.11.00.54.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Mar 2026 00:54:22 -0700 (PDT) Message-ID: <4242ff70-c5d4-40f4-bddb-c823675fcb4c@suse.com> Date: Wed, 11 Mar 2026 08:54:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/5] Introduce QPW for per-cpu operations (v2) Content-Language: en-US To: Marcelo Tosatti , Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Leonardo Bras , Thomas Gleixner , Waiman Long , Boqun Feun , Mel Gorman References: <20260302154945.143996316@redhat.com> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 70ED340004 X-Stat-Signature: q8n5gebobpoa9a8qey9h6ys4xbipz6pw X-Rspam-User: X-HE-Tag: 1773215664-232197 X-HE-Meta: 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 7bW7HpK1 0pw8+mucKMicpi8vcg0CS0rpUqyr3ckLiEWVViCzfUTM7YGWQtdrXW5yx7N8dhb6LoBWNX/58k7dFG3DGVGQzJ9dcgsbVR4Db3It4AcHkORtYz0xSWfZp7EkbUCSTTPiz5z7OapNV7Df/0ryeu1vCp9QngEkDNc7Pc6UKO0AI2xqMQCAJCF8oUI2qImdu4tmQ0hTKRNHG+Nf/mtsB2AxXyCFTBD6AX7KQcX/qTbYoal537kjDlZ3RiBDMXoEFcIKrDj+OEHT5OTqqBaDroWzeILBtufEbbRsJTo+eyiw75qerfsOsXzDVvPlidygtGW2X4Fw6/D+WT9VQ7SGjoPEZpRXZlUyphylotLY5D2yalJkgXFYyoDZCJ5EqnZCBnv9867kzIQWpLphO8zKV4agIXSwDzwL57gQTVm6kywHO6KHY21c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/10/26 18:12, Marcelo Tosatti wrote: > Hi Frederic, > > On Thu, Mar 05, 2026 at 05:55:12PM +0100, Frederic Weisbecker wrote: > > Can you please be more verbose, mindful of lesser cognitive powers ? :-) > > Note: i also dislike the added layers (and multiple cases) QPW adds. > > But there is precedence with local locks... > > Code would be less complex in case spinlocks were added: > > 01b44456a7aa7c3b24fa9db7d1714b208b8ef3d8 mm/page_alloc: replace local_lock with normal spinlock > 4b23a68f953628eb4e4b7fe1294ebf93d4b8ceee mm/page_alloc: protect PCP lists with a spinlock Note that per bf75f200569dd05ac2112797f44548beb6b4be26 changelog this seems it was all done for the same reasons as QPW. It's nice we got the trylock-without-irqsave approach as a followup, but the cost of (especially non-inlined) spin_trylock is not great, given that now we could do the trylock-without-irqsave cheaply with local_trylock. So that to me suggests it could be worth to try convert pcplists to QPW if it's agreed upon as the best way forward and is merged. > But people seem to reject that in the basis of performance > degradation. >