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Re: Question about madvise(DONTNEED) in glibc malloc


OndÅej BÃlka, le Mon 15 Apr 2013 12:14:39 +0200, a Ãcrit :
> On Sun, Apr 14, 2013 at 10:11:50PM -0700, KOSAKI Motohiro wrote:
> > (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.
> 
> A SIGBUS makes using vrange out of question. We simply cannot ignore user generated SIGBUS.

Such SIGBUS would not happen unless the user accesses some freed memory,
which he shouldn't be doing anyway.

Samuel


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