Re: [RFC] Support volatile range for anon vma

[Minchan Kim]

Hi Christoph,

On Thu, Nov 01, 2012 at 08:26:09PM +0000, Christoph Lameter wrote:
> On Fri, 26 Oct 2012, Minchan Kim wrote:
> 
> > I guess it would improve system performance very well.
> > But as I wrote down in description, downside of the patch is that we have to
> > age anon lru although we don't have swap. But gain via the patch is bigger than
> > loss via aging of anon lru when memory pressure happens. I don't see other downside
> > other than it. What do you think about it?
> > (I didn't implement anon lru aging in case of no-swap but it's trivial
> > once we decide)
> 
> 
> I am a bit confused like some of the others as to why this patch is
> necessary since we already have DONT_NEED.

Totally, my fault. I should have written clearly.

DONT_NEED have to zap all pte entries/tlb flush when system call
happens so DONT_NEED isn't cheap.
Even, later if user accesses address again, page fault happens.

This patch is to remove above two overheads.
while I discussed with KOSAKI, I found there was trial of simillar
goal by Rik. https://lkml.org/lkml/2007/4/17/53
But as I look over the code, it seems to have a cost about setting PG_lazyfree
on all pages of range which isn't in my implementation.

Anyway, I would like to know where Rik's patch wasn't merged at that time.

> 
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-- 
Kind regards,
Minchan Kim
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