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Re: Question about madvise(DONTNEED) in glibc malloc


(4/14/13 9:12 PM), Siddhesh Poyarekar wrote:
> On 14 April 2013 22:07, KOSAKI Motohiro <kosaki.motohiro@gmail.com> wrote:
>> Now, we linux MM folks discuss are discussing about new memory discarding feature.
>> (https://lkml.org/lkml/2013/3/12/105). The motivation is similar wtih MADV_FREE,
>> but more efficient. (http://lwn.net/Articles/230799)
> 
> I just went through this and it looks interesting as a replacement for
> MADV_DONTNEED in malloc.  Please let us know what becomes of this so
> that we could explore the possibility of using it in malloc.

Firstly, this api is still under discusstion and any feedback has a chance to change 
api design.

The idea is simple. vrange(VOLATILE) just mark the argument pages is discardable. but
doesn't discard. No page table walk, No TLB shootdown, No anything more.
Touching the VOLATILed range, makes SIGBUG. you need to call vrange(NOVOLATILE) because
you begin to use again.
When kernel meet memory starvation, kerenl may discared VOLATILed pages instead of swap
out. Of cource, jsut dropping is much faster than disk write. More importantly, as far as
system has enough memory, this heaviy weight pte nuke never run.

Please feel free to ask everything. We add more document to the man page or change the design.



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