Re: [RFC v2] Support volatile range for anon vma

[Minchan Kim]

Hello,

On Mon, Nov 05, 2012 at 03:54:43PM -0800, Arun Sharma wrote:
> On Wed, Oct 31, 2012 at 06:56:05PM -0400, KOSAKI Motohiro wrote:
> > glibc malloc discard freed memory by using MADV_DONTNEED
> > as tcmalloc. and it is often a source of large performance decrease.
> > because of MADV_DONTNEED discard memory immediately and
> > right after malloc() call fall into page fault and pagesize memset() path.
> > then, using DONTNEED increased zero fill and cache miss rate.
> 
> The memcg based solution that I posted a few months ago is working well
> for us. We see significantly less cpu in zero'ing pages.
> 
> Not everyone was comfortable with the security implications of recycling
> pages between processes in a memcg, although it was disabled by default
> and had to be explicitly opted-in.
> 
> Also, memory allocators have a second motivation in using madvise: to
> create virtually contiguous regions of memory from a fragmented address 
> space, without increasing the RSS.

I don't get it. How do we create contiguos region by madvise?
Just out of curiosity.
Could you elaborate that use case? :)

> 
>  -Arun
> 
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-- 
Kind Regards,
Minchan Kim
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