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Wed, 11 Mar 2026 09:18:22 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 9687306816499 X-SMAIL-UIID: 7E0815E5776D42F09DEB167BE80166DC-20260311-091822-1 From: Hillf Danton To: Marcelo Tosatti Cc: Frederic Weisbecker , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Christoph Lameter , Vlastimil Babka Subject: Re: [PATCH v2 0/5] Introduce QPW for per-cpu operations (v2) Date: Wed, 11 Mar 2026 09:18:14 +0800 Message-ID: <20260311011815.785-1-hdanton@sina.com> In-Reply-To: References: <20260302154945.143996316@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 196E740005 X-Stat-Signature: nx9t8egpjkmhougn8err4q9agzegtndz X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1773191907-399908 X-HE-Meta: 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 2tKm6Low M6FI+pSrPDwaa9SaP3BYfr8crW0vH8v8umWkkbWjJc7WiC9A5lEQgAfQAgG76u5rUcXNwRBz6CbKUk5nolO1KmPuPx1s02GsUfkJQVlb+iRB0mD1gvZM8lo8Wkax7FQWNbS0yTOkvRlkjlIFEruJVodxcPryOKNtgZV6EYaIqaKODvw8BOF3ZUerzMK/bEX5Cr8Mze0X7fh3ksPXozLaZ7elw1RIFM/nPoseD4hiHoje7ndsUWX94jI7djjNinV214jbrwo/MXic9Ca0R1oJO7M0Ebg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 10 Mar 2026 14:12:03 -0300 Marcelo Tosatti 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 > > But people seem to reject that in the basis of performance degradation. > Given pcp_spin_lock() cut in 0f21b911011f ("mm/page_alloc: simplify and cleanup pcp locking"), spin lock works because of trylock and fallback, so it is a special case instead of a generic boilerplate to follow.