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Message-ID: <682380ba-c8f3-4023-928c-2152e934f8db@kernel.org>
Date: Tue, 3 Mar 2026 13:03:36 +0100
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Subject: Re: [PATCH v2 2/5] Introducing qpw_lock() and per-cpu queue & flush
 work
Content-Language: en-US
To: Marcelo Tosatti <mtosatti@redhat.com>, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>,
 Roman Gushchin <roman.gushchin@linux.dev>,
 Shakeel Butt <shakeel.butt@linux.dev>, Muchun Song <muchun.song@linux.dev>,
 Andrew Morton <akpm@linux-foundation.org>, Christoph Lameter <cl@linux.com>,
 Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>,
 Joonsoo Kim <iamjoonsoo.kim@lge.com>, Hyeonggon Yoo <42.hyeyoo@gmail.com>,
 Leonardo Bras <leobras.c@gmail.com>, Thomas Gleixner <tglx@linutronix.de>,
 Waiman Long <longman@redhat.com>, Boqun Feun <boqun.feng@gmail.com>,
 Frederic Weisbecker <frederic@kernel.org>
References: <20260302154945.143996316@redhat.com>
 <20260302155105.214878062@redhat.com>
From: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
In-Reply-To: <20260302155105.214878062@redhat.com>
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On 3/2/26 16:49, Marcelo Tosatti wrote:
> +#define local_qpw_lock(lock)								\
> +	do {										\
> +		if (static_branch_maybe(CONFIG_QPW_DEFAULT, &qpw_sl)) {			\
> +			migrate_disable();						\

Have you considered using migrate_disable() on PREEMPT_RT and
preempt_disable() on !PREEMPT_RT since it's cheaper? It's what the pcp
locking in mm/page_alloc.c does, for that reason. It should reduce the
overhead with qpw=1 on !PREEMPT_RT.

> +			spin_lock(this_cpu_ptr(lock.sl));				\
> +		} else									\
> +			local_lock(lock.ll);						\
> +	} while (0)
> +