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a="198505230" X-IronPort-AV: E=Sophos;i="5.82,319,1613462400"; d="scan'208";a="198505230" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2021 15:44:52 -0700 IronPort-SDR: hPOy5o5jtVUZN4Cx027K97zYJf7w6YbFDuiX6t3Q8++aLrySPl8xbXidokjVMAzYnlgbUgy6x6 2vNi4NZ5eKTQ== X-IronPort-AV: E=Sophos;i="5.82,319,1613462400"; d="scan'208";a="441126837" Received: from djayapra-mobl2.amr.corp.intel.com (HELO [10.212.209.34]) ([10.212.209.34]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2021 15:44:52 -0700 Subject: Re: [PATCH 5/6] mm/page_alloc: Limit the number of pages on PCP lists when reclaim is active To: Mel Gorman , Linux-MM Cc: Dave Hansen , Matthew Wilcox , Vlastimil Babka , Michal Hocko , Nicholas Piggin , LKML References: <20210521102826.28552-1-mgorman@techsingularity.net> <20210521102826.28552-6-mgorman@techsingularity.net> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210521102826.28552-6-mgorman@techsingularity.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/21/21 3:28 AM, Mel Gorman wrote: > +static int nr_pcp_high(struct per_cpu_pages *pcp, struct zone *zone) > +{ > + int high = READ_ONCE(pcp->high); > + > + if (unlikely(!high)) > + return 0; > + > + if (!test_bit(ZONE_RECLAIM_ACTIVE, &zone->flags)) > + return high; > + > + /* > + * If reclaim is active, limit the number of pages that can be > + * stored on pcp lists > + */ > + return READ_ONCE(pcp->batch) << 2; > +} Should there be a sanity check on this? Let's say we had one of those weirdo zones with tons of CPUs and a small low_wmark_pages(). Could we have a case where: pcp->high < pcp->batch<<2 and this effectively *raises* nr_pcp_high()? It's not possible with the current pcp->high calculation, but does anything prevent it now?