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[209.132.183.28]) by mx.google.com with ESMTPS id a74si1238754qkb.123.2019.06.14.00.25.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Jun 2019 00:25:18 -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-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 61DA930917AF; Fri, 14 Jun 2019 07:25:17 +0000 (UTC) Received: from [10.36.116.252] (ovpn-116-252.ams2.redhat.com [10.36.116.252]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8E6E3648C8; Fri, 14 Jun 2019 07:24:56 +0000 (UTC) Subject: Re: [RFC][Patch v10 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, mst@redhat.com, dodgen@google.com, konrad.wilk@oracle.com, dhildenb@redhat.com, aarcange@redhat.com, alexander.duyck@gmail.com References: <20190603170306.49099-1-nitesh@redhat.com> <20190603170306.49099-2-nitesh@redhat.com> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190603170306.49099-2-nitesh@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Fri, 14 Jun 2019 07:25:17 +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 03.06.19 19:03, Nitesh Narayan Lal wrote: > This patch introduces the core infrastructure for free page hinting in > virtual environments. It enables the kernel to track the free pages which > can be reported to its hypervisor so that the hypervisor could > free and reuse that memory as per its requirement. > > While the pages are getting processed in the hypervisor (e.g., > via MADV_FREE), the guest must not use them, otherwise, data loss > would be possible. To avoid such a situation, these pages are > temporarily removed from the buddy. The amount of pages removed > temporarily from the buddy is governed by the backend(virtio-balloon > in our case). > > To efficiently identify free pages that can to be hinted to the > hypervisor, bitmaps in a coarse granularity are used. Only fairly big > chunks are reported to the hypervisor - especially, to not break up THP > in the hypervisor - "MAX_ORDER - 2" on x86, and to save space. The bits > in the bitmap are an indication whether a page *might* be free, not a > guarantee. A new hook after buddy merging sets the bits. > > Bitmaps are stored per zone, protected by the zone lock. A workqueue > asynchronously processes the bitmaps, trying to isolate and report pages > that are still free. The backend (virtio-balloon) is responsible for > reporting these batched pages to the host synchronously. Once reporting/ > freeing is complete, isolated pages are returned back to the buddy. > > There are still various things to look into (e.g., memory hotplug, more > efficient locking, possible races when disabling). > > Signed-off-by: Nitesh Narayan Lal > --- > drivers/virtio/Kconfig | 1 + > include/linux/page_hinting.h | 46 +++++++ > mm/Kconfig | 6 + > mm/Makefile | 2 + > mm/page_alloc.c | 17 +-- > mm/page_hinting.c | 236 +++++++++++++++++++++++++++++++++++ > 6 files changed, 301 insertions(+), 7 deletions(-) > create mode 100644 include/linux/page_hinting.h > create mode 100644 mm/page_hinting.c > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig > index 35897649c24f..5a96b7a2ed1e 100644 > --- a/drivers/virtio/Kconfig > +++ b/drivers/virtio/Kconfig > @@ -46,6 +46,7 @@ config VIRTIO_BALLOON > tristate "Virtio balloon driver" > depends on VIRTIO > select MEMORY_BALLOON > + select PAGE_HINTING > ---help--- > This driver supports increasing and decreasing the amount > of memory within a KVM guest. BTW, this hunk belongs to the virtio-balloon patch. -- Thanks, David / dhildenb