This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: Question about madvise(DONTNEED) in glibc malloc
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>
- Cc: Siddhesh Poyarekar <siddhesh dot poyarekar at gmail dot com>, libc-alpha <libc-alpha at sourceware dot org>
- Date: Mon, 15 Apr 2013 12:14:39 +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>
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.
I do not see how we could distinguish user/vrange SIGBUS.
> 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.
>