linux-kernel - Re: x86: vmalloc and THP

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Message-ID: <1407846532.10122.66.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 12 Aug 2014 05:28:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Oren Twaig <oren@...lemp.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org,
	"Shai Fultheim (Shai@...leMP.com)" <Shai@...lemp.com>
Subject: Re: x86: vmalloc and THP

On Tue, 2014-08-12 at 09:07 +0300, Kirill A. Shutemov wrote:
> On Tue, Aug 12, 2014 at 08:00:54AM +0300, Oren Twaig wrote:

> >Does memory allocated using vmalloc() will be mapped using huge
> >pages either directly or later by THP ? 
> 
> No. It's neither aligned properly, nor physically contiguous.
> 
> >If not, is there any fast way to change this behavior ? Maybe by
> >changing the granularity/alignment of such allocations to allow such
> >mapping ?
> 
> What's the point to use vmalloc() in this case?

Look at various large hashes we have in the system, all using
vmalloc() :

[    0.006856] Dentry cache hash table entries: 16777216 (order: 15, 134217728 bytes)
[    0.033130] Inode-cache hash table entries: 8388608 (order: 14, 67108864 bytes)
[    1.197621] TCP established hash table entries: 524288 (order: 11, 8388608 bytes)

I would imagine a performance difference if we were using hugepages.



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