Re: speed difference between using hard-linked and modular drives?

[Anton Blanchard]

> > we should fix this by trying to allocate continuous physical memory if
> > possible, and fall back to vmalloc() only if this allocation fails.
> 
> Check -aa. A patch to do that has been in there for some time now.

We also need a way to satisfy very large allocations for the hashes (eg
the pagecache hash). On a 32G machine we get awful performance on the
pagecache hash because we can only get an order 9 allocation out of
get_free_pages:

http://samba.org/~anton/linux/pagecache/pagecache_before.png

When switching to vmalloc the hash is large enough to be useful:

http://samba.org/~anton/linux/pagecache/pagecache_after.png

As pointed out by Davem and Ingo we should try and avoid vmalloc here
due to tlb trashing.

Anton