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Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting
To:     "Wang, Wei W" <wei.w.wang@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "lcapitulino@redhat.com" <lcapitulino@redhat.com>,
        "pagupta@redhat.com" <pagupta@redhat.com>,
        "yang.zhang.wz@gmail.com" <yang.zhang.wz@gmail.com>,
        "riel@surriel.com" <riel@surriel.com>,
        "david@redhat.com" <david@redhat.com>,
        "mst@redhat.com" <mst@redhat.com>,
        "dodgen@google.com" <dodgen@google.com>,
        "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
        "dhildenb@redhat.com" <dhildenb@redhat.com>,
        "aarcange@redhat.com" <aarcange@redhat.com>
References: <20190204201854.2328-1-nitesh@redhat.com>
 <286AC319A985734F985F78AFA26841F73DF6B56A@shsmsx102.ccr.corp.intel.com>
From:   Nitesh Narayan Lal <nitesh@redhat.com>
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Organization: Red Hat Inc,
Message-ID: <f9516222-793a-a169-c18a-728ca0256cd3@redhat.com>
Date:   Wed, 13 Feb 2019 07:06:32 -0500
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Content-Type: multipart/mixed; boundary="PLnnUTd4vEqoEphvcp8R9SJ7Y1kub4KsV";
 protected-headers="v1"
From: Nitesh Narayan Lal <nitesh@redhat.com>
To: "Wang, Wei W" <wei.w.wang@intel.com>,
 "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
 "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 "pbonzini@redhat.com" <pbonzini@redhat.com>,
 "lcapitulino@redhat.com" <lcapitulino@redhat.com>,
 "pagupta@redhat.com" <pagupta@redhat.com>,
 "yang.zhang.wz@gmail.com" <yang.zhang.wz@gmail.com>,
 "riel@surriel.com" <riel@surriel.com>, "david@redhat.com"
 <david@redhat.com>, "mst@redhat.com" <mst@redhat.com>,
 "dodgen@google.com" <dodgen@google.com>,
 "konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
 "dhildenb@redhat.com" <dhildenb@redhat.com>,
 "aarcange@redhat.com" <aarcange@redhat.com>
Message-ID: <f9516222-793a-a169-c18a-728ca0256cd3@redhat.com>
Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting
References: <20190204201854.2328-1-nitesh@redhat.com>
 <286AC319A985734F985F78AFA26841F73DF6B56A@shsmsx102.ccr.corp.intel.com>
In-Reply-To: <286AC319A985734F985F78AFA26841F73DF6B56A@shsmsx102.ccr.corp.intel.com>

--PLnnUTd4vEqoEphvcp8R9SJ7Y1kub4KsV
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Language: en-US


On 2/13/19 4:00 AM, Wang, Wei W wrote:
> On Tuesday, February 5, 2019 4:19 AM, Nitesh Narayan Lal wrote:
>> The following patch-set proposes an efficient mechanism for handing fr=
eed
>> memory between the guest and the host. It enables the guests with no p=
age
>> cache to rapidly free and reclaims memory to and from the host respect=
ively.
>>
>> Benefit:
>> With this patch-series, in our test-case, executed on a single system =
and
>> single NUMA node with 15GB memory, we were able to successfully launch=

>> atleast 5 guests when page hinting was enabled and 3 without it. (Deta=
iled
>> explanation of the test procedure is provided at the bottom).
>>
>> Changelog in V8:
>> In this patch-series, the earlier approach [1] which was used to captu=
re and
>> scan the pages freed by the guest has been changed. The new approach i=
s
>> briefly described below:
>>
>> The patch-set still leverages the existing arch_free_page() to add thi=
s
>> functionality. It maintains a per CPU array which is used to store the=
 pages
>> freed by the guest. The maximum number of entries which it can hold is=

>> defined by MAX_FGPT_ENTRIES(1000). When the array is completely filled=
, it
>> is scanned and only the pages which are available in the buddy are sto=
red.
>> This process continues until the array is filled with pages which are =
part of
>> the buddy free list. After which it wakes up a kernel per-cpu-thread.
>> This kernel per-cpu-thread rescans the per-cpu-array for any re-alloca=
tion
>> and if the page is not reallocated and present in the buddy, the kerne=
l
>> thread attempts to isolate it from the buddy. If it is successfully is=
olated, the
>> page is added to another per-cpu array. Once the entire scanning proce=
ss is
>> complete, all the isolated pages are reported to the host through an e=
xisting
>> virtio-balloon driver.
> The free page is removed from the buddy list here. When will they get r=
eturned to the buddy list so that the guest threads can use them normally=
?
Once the host free the pages. All the isolated pages are returned back
to the buddy. (This is implemented in hyperlist_ready())
>
> Best,
> Wei
--=20
Regards
Nitesh


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