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[209.132.183.28]) by mx.google.com with ESMTPS id d207si10697142qkc.51.2019.07.15.07.40.46 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Jul 2019 07:40:46 -0700 (PDT) Received-SPF: pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of david@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 92433309175E; Mon, 15 Jul 2019 14:40:45 +0000 (UTC) Received: from [10.36.118.52] (unknown [10.36.118.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id 781AD5D9C8; Mon, 15 Jul 2019 14:40:31 +0000 (UTC) Subject: Re: [RFC][Patch v11 1/2] mm: page_hinting: core infrastructure From: David Hildenbrand To: Dave Hansen , 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, 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> <46336efb-3243-0083-1d20-7e8578131679@redhat.com> Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <46336efb-3243-0083-1d20-7e8578131679@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Mon, 15 Jul 2019 14:40:45 +0000 (UTC) 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 15.07.19 11:33, David Hildenbrand wrote: > On 11.07.19 20:21, Dave Hansen wrote: >> 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. >> > > I don't think it's incorrect, it's just not optimal in all scenarios. > E.g., in you example, this approach would "waste" 2 * 1GB of tracking > data for the wholes (2* 64bytes when using 1 bit for 2MB). > > FWIW, this is not a numa-specific thingy. We can have sparse zones > easily on single-numa systems. > > Node: 0 > NORMAL 0->1GB, 2->3GB > MOVABLE 1->2GB, 3->4GB > > So tracking it per zones instead instead of zone type is only one part > of the story. > Oh, and FWIW, in setups like Node: 0 1 NORMAL 4->5GB, 6->7GB 5->6GB, 8->9GB What Nitesh proposes is actually better. So it really depends on the use case - but in general sparsity is the issue. -- Thanks, David / dhildenb