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Re: Question about madvise(DONTNEED) in glibc malloc
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: Samuel Thibault <samuel dot thibault at ens-lyon dot org>
- Cc: KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>, Siddhesh Poyarekar <siddhesh dot poyarekar at gmail dot com>, libc-alpha <libc-alpha at sourceware dot org>
- Date: Mon, 15 Apr 2013 14:35:04 +0200
- Subject: Re: Question about madvise(DONTNEED) in glibc malloc
- References: <516ADB3C dot 9040805 at gmail dot com> <CAAHN_R23vHH4B_=GUHFXAfcRL5gFrOp6dyBLcskCQNG5VswxAA at mail dot gmail dot com> <516B8C16 dot 1050802 at gmail dot com> <20130415101439 dot GA3110 at domone dot kolej dot mff dot cuni dot cz> <20130415111319 dot GB6152 at type dot bordeaux dot inria dot fr> <20130415121141 dot GA10611 at domone dot kolej dot mff dot cuni dot cz> <20130415121508 dot GF6152 at type dot bordeaux dot inria dot fr>
On Mon, Apr 15, 2013 at 02:15:08PM +0200, Samuel Thibault wrote:
> OndÅej BÃlka, le Mon 15 Apr 2013 14:11:41 +0200, a Ãcrit :
> > On Mon, Apr 15, 2013 at 01:13:19PM +0200, Samuel Thibault wrote:
> > > 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.
> >
> > When kill -BUS pid became illegal?
>
> I don't understand how that relates to what we are talking about. I've
> never said sending -BUS was illegal. I've said that accessing freed
> memory is illegal.
Accessing freed memory is illegal but not only way how that SIGBUS could
happen. It could be SIGBUS from kill which is perfectly legal.
>
> Samuel