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23 Jan 2020 09:20:15 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,354,1574150400"; d="scan'208";a="229923390" Received: from unknown (HELO [10.7.201.139]) ([10.7.201.139]) by orsmga006.jf.intel.com with ESMTP; 23 Jan 2020 09:20:15 -0800 Subject: Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting To: Alexander Duyck , Alexander Graf , Alexander Duyck , kvm@vger.kernel.org, mst@redhat.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, mgorman@techsingularity.net, vbabka@suse.cz, "Van De Ven, Arjan" Cc: yang.zhang.wz@gmail.com, nitesh@redhat.com, konrad.wilk@oracle.com, david@redhat.com, pagupta@redhat.com, riel@surriel.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, osalvador@suse.de, "Paterson-Jones, Roland" , hannes@cmpxchg.org, hare@suse.com, "Boeuf, Sebastien" References: <20200122173040.6142.39116.stgit@localhost.localdomain> <914aa4c3-c814-45e0-830b-02796b00b762@amazon.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/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 1/23/20 8:26 AM, Alexander Duyck wrote: >> The big piece I'm missing is the page cache. Linux will by default try= =20 >> to keep the free list as small as it can in favor of page cache, so mo= st=20 >> of the benefit of this patch set will be void in real world scenarios. > Agreed. This is a the next piece of this I plan to work on once this is > accepted. For now the quick and dirty approach is to essentially make u= se > of the /proc/sys/vm/drop_caches interface in the guest by either puttin= g > it in a cronjob somewhere or to have it after memory intensive workload= s. There was an implementation in "Clear Linux" that used this sysctl: > https://github.com/Conan-Kudo/omv-kernel-rc/blob/master/0154-sysctl-vm-= Fine-grained-cache-shrinking.patch (I can't find it in the Clear repos at the moment, must not be used currently). But the idea was to have a little daemon in the host that periodically applied some artificial pressure with this sysctl. This sysctl is a smaller hammer than /proc/sys/vm/drop_caches and lets you drop small amounts of cache. The right way to do it is probably to do real, generic reclaim instead of drop_caches. This isn't conceptually *that* far away from the "proactive reclaim" that other folks have proposed: https://lwn.net/Articles/787611/