Re: [mm][RFC][PATCH 0/11] mm accessor updates.

KAMEZAWA Hiroyuki
2009-12-16T10:16:24Z

On Wed, 16 Dec 2009 11:11:07 +0100
Andi Kleen <andi@firstfloor.org> wrote:

> On Wed, Dec 16, 2009 at 12:00:11PM +0900, KAMEZAWA Hiroyuki wrote:
> > This is from Christoph Lameter's mm_accessor patch posted 5/Nov.
> >
> > Replacing all access to mm->mmap_sem with mm-accessor functions as
> > mm_read_lock,
> > mm_write_lock,
> > etc...
> >
> > This kind of function allows us to improve page fault performance etc..
> > For example, skil down_read(mmap_sem) in some situation.
> > (as: http://marc.info/?l=linux-mm&m=125809791306459&w=2)
>
> The problem is that it also slows down the writers, and we have
> some workloads where writing is the bottleneck.
>
> I don't think this is the right trade off at this time.
>
Maybe you don't see my patch. (above URL) no slow down to write side.
My one doesn't use percpu counter.

> Also the patches didn't fare too well in testing unfortunately.
>
> I suspect we'll rather need multiple locks split per address
> space range.

This set doesn't include any changes of the logic. Just replace all mmap_sem.
I think this is good start point (for introducing another logic etc..)

Thanks,
-Kame