Re: x86: vmalloc and THP

Eric Dumazet
2014-08-12T12:28:54Z

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.