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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=d7BZOv6y; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 861F5606A32C; Thu, 5 Nov 2026 09:58:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=d7BZOv6y Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7802A1F000C1; Thu, 5 Nov 2026 09:58:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793872733; bh=q/X+C1Y8TceHHEUuqIf1Y7YzjYQg0qCuJDWINnus5m0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=d7BZOv6y47/RQ2Ml9iy4bi7L5V1/nD//V4d6VP/9soB5stou23M4Km74Szg3Nrm3p wCdMVRys8gcsqkPoyJyNnyL1U0/e2hdmDU2HkeQ3y++ZKgCL6NIKS2g+Xn1qVYUCIg /JOTkot7nWIHdNJmFwZ4NZYbrxBMA0spOxrsxhXtH4/7hCzWTyA9FMG0FQNRAqRlDC S8+JrNV0DEVmot9dYaua6ajAf7G92UMTuXxCX6VowkUJYKFOPGS0mBCz7JpMALgdFe ComZLv0SAKpc6/Opp4e7FLf0nsKozgFIVdJJK+EDJLejPETCTHHNJclf5I4qzf7mOg xnE9UCMW3swNA== Message-ID: <6c5f3ef1-188f-4a5d-8775-578dc2c84c59@kernel.org> Date: Thu, 5 Nov 2026 10:58:42 +0100 X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 02/12] mm/page_alloc: keep the pagesets of an empty zone Content-Language: en-US To: Zi Yan , "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baoquan.he@linux.dev, baolin.wang@linux.alibaba.com, rientjes@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, muchun.song@linux.dev, osalvador@suse.de, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, bigeasy@linutronix.de, clrkwllms@kernel.org, nathan@kernel.org, ndesaulniers@google.com, morbo@google.com, justinstitt@google.com, Bessel.Wang@huawei.com, jiang.liu@huawei.com, mgorman@techsingularity.net, anshuman.khandual@arm.com, Josef Bacik , stable@vger.kernel.org References: <20261101021340.2251928-1-gourry@gourry.net> <20261101021340.2251928-3-gourry@gourry.net> <489b668a-033c-4161-93e8-15d6b9b28b51@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/3/26 17:04, Zi Yan wrote: > On Tue Nov 3, 2026 at 9:57 AM EST, Vlastimil Babka (SUSE) wrote: >>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>> index f1048168c90c..1850a41f24f7 100644 >>>> --- a/mm/page_alloc.c >>>> +++ b/mm/page_alloc.c >>>> @@ -6308,6 +6308,10 @@ void __meminit setup_zone_pageset(struct zone *zone) >>>> { >>>> int cpu; >>>> >>>> + /* The zone has been populated before, see zone_pcp_reset(). */ >>>> + if (zone->per_cpu_pageset != &boot_pageset) >>>> + return; >>>> + >>>> /* Size may be 0 on !SMP && !NUMA */ >>>> if (sizeof(struct per_cpu_zonestat) > 0) >>>> zone->per_cpu_zonestats = alloc_percpu(struct per_cpu_zonestat); >>>> @@ -6400,6 +6404,10 @@ void __init setup_per_cpu_pageset(void) >>>> >>>> __meminit void zone_pcp_init(struct zone *zone) >>>> { >>>> + /* A node which is added again, see zone_pcp_reset(). */ >>> >>> it might be better to explain zone->per_cpu_pageset can only be NULL at >>> boot time and it needs an initialization. >> >> Hmm. >> >>>> + if (zone->per_cpu_pageset && zone->per_cpu_pageset != &boot_pageset) >>>> + return; >> >> Shouldn't then the check be just: >> >> if (zone->per_cpu_pageset) >> return; >> >> Because if it's == &boot_pageset, we are just setting the same values that >> area already there? >> > > Right. And zone_pcp_init(), called by zone_init_internals(), becomes a nop for > free_area_init_core_hotplug(). Then I wonder if zone_init_internals() is > needed for hotplug, but that belongs to a later cleanup. Yep, that's for later cleanup. Right now the minimum that's correct and not unnecessarily misleading is enough. So I've done this: diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 1850a41f24f7..20bfd11c5851 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -6404,8 +6404,8 @@ void __init setup_per_cpu_pageset(void) __meminit void zone_pcp_init(struct zone *zone) { - /* A node which is added again, see zone_pcp_reset(). */ - if (zone->per_cpu_pageset && zone->per_cpu_pageset != &boot_pageset) + /* This initialization only needs to be done once */ + if (zone->per_cpu_pageset) return; /*