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[192.55.52.120]) by mx.google.com with ESMTPS id q187si5493588pga.220.2019.07.11.11.21.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Jul 2019 11:21:50 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.120 as permitted sender) client-ip=192.55.52.120; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Jul 2019 11:21:50 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,479,1557212400"; d="scan'208";a="156901295" Received: from ray.jf.intel.com (HELO [10.7.201.139]) ([10.7.201.139]) by orsmga007.jf.intel.com with ESMTP; 11 Jul 2019 11:21:49 -0700 Subject: Re: [RFC][Patch v11 1/2] mm: page_hinting: core infrastructure To: Nitesh Narayan Lal , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, pbonzini@redhat.com, lcapitulino@redhat.com, pagupta@redhat.com, wei.w.wang@intel.com, yang.zhang.wz@gmail.com, riel@surriel.com, david@redhat.com, mst@redhat.com, dodgen@google.com, konrad.wilk@oracle.com, dhildenb@redhat.com, aarcange@redhat.com, alexander.duyck@gmail.com, john.starks@microsoft.com, mhocko@suse.com References: <20190710195158.19640-1-nitesh@redhat.com> <20190710195158.19640-2-nitesh@redhat.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190710195158.19640-2-nitesh@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 7/10/19 12:51 PM, Nitesh Narayan Lal wrote: > +static void bm_set_pfn(struct page *page) > +{ > + struct zone *zone = page_zone(page); > + int zone_idx = page_zonenum(page); > + unsigned long bitnr = 0; > + > + lockdep_assert_held(&zone->lock); > + bitnr = pfn_to_bit(page, zone_idx); > + /* > + * TODO: fix possible underflows. > + */ > + if (free_area[zone_idx].bitmap && > + bitnr < free_area[zone_idx].nbits && > + !test_and_set_bit(bitnr, free_area[zone_idx].bitmap)) > + atomic_inc(&free_area[zone_idx].free_pages); > +} Let's say I have two NUMA nodes, each with ZONE_NORMAL and ZONE_MOVABLE and each zone with 1GB of memory: Node: 0 1 NORMAL 0->1GB 2->3GB MOVABLE 1->2GB 3->4GB This code will allocate two bitmaps. The ZONE_NORMAL bitmap will represent data from 0->3GB and the ZONE_MOVABLE bitmap will represent data from 1->4GB. That's the result of this code: > + if (free_area[zone_idx].base_pfn) { > + free_area[zone_idx].base_pfn = > + min(free_area[zone_idx].base_pfn, > + zone->zone_start_pfn); > + free_area[zone_idx].end_pfn = > + max(free_area[zone_idx].end_pfn, > + zone->zone_start_pfn + > + zone->spanned_pages); But that means that both bitmaps will have space for PFNs in the other zone type, which is completely bogus. This is fundamental because the data structures are incorrectly built per zone *type* instead of per zone.