linux-kernel - Re: [PATCHv7 00/29] THP-enabled tmpfs/shmem using compound pages

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Date:	Mon, 25 Apr 2016 06:30:01 -0700
From:	Andres Lagar-Cavilla <andreslc@...gle.com>
To:	Wincy Van <fanwenyi0529@...il.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	"Shi, Yang" <yang.shi@...aro.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Ning Qu <quning@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCHv7 00/29] THP-enabled tmpfs/shmem using compound pages

On Sat, Apr 23, 2016 at 10:46 PM, Wincy Van <fanwenyi0529@...il.com> wrote:
> On Wed, Apr 20, 2016 at 1:07 AM, Andres Lagar-Cavilla
> <andreslc@...gle.com> wrote:
>> Andrea, we provide the, ahem, adjustments to
>> transparent_hugepage_adjust. Rest assured we aggressively use mmu
>> notifiers with no further changes required.
>>
>> As in: zero changes have been required in the lifetime (years) of
>> kvm+huge tmpfs at Google, other than mod'ing
>> transparent_hugepage_adjust.
>
> We are using kvm + tmpfs to do qemu live upgrading, how does google
> use this memory model ?
> I think our pupose to use tmpfs may be the same.

Nothing our of the ordinary. Guest memory is an mmap of a tmpfs fd.
Huge tmpfs gives us naturally a great guest performance boost.
MAP_SHARED, and having guest memory persist any one given process, are
what drives us to use tmpfs.

Andres
>
> And huge tmpfs is a really good improvement for that.
>
>>
>> As noted by Paolo, the additions to transparent_hugepage_adjust could
>> be lifted outside of kvm (into shmem.c? maybe) for any consumer of
>> huge tmpfs with mmu notifiers.
>>
>
> Thanks,
> Wincy



-- 
Andres Lagar-Cavilla | Google Kernel Team | andreslc@...gle.com