Re: [patch] mm: reduce pagetable-freeing latencies

[Hugh Dickins <hugh@veritas.com>]

On Wed, 25 Jul 2007, Benjamin Herrenschmidt wrote:
> 
> In fact, i discussed with peter and I think the best is to only have one
> entry in the stack mmu_gather structure.

Four or eight would be much nicer than one, but you're right there's
a stackdepth worry: good spotting of those unmap_mapping_range cases,
I'd certainly been thinking we were fairly near the top of the stack
in unmap_vmas, which is not so (or not obviously so) in those cases.

> If we fail to allocate a page
> to batch entries, we flush that one and steal it :-) Then we have a page
> to gather more.

That will often be the case for anonymous pages, but not for pagecache
pages.  I had wondered whether to make exit_mmap unmap the stack first
(rather than text first as usually happens), but seems rather a hack.

Hugh