Re: x86: vmalloc and THP

[Eric Dumazet]

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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