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RE: [Xen-devel] [PATCH][TOOLS] Reducing impactofdomainsave/restore/dump on Dom0

  • To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Graham, Simon" <Simon.Graham@xxxxxxxxxxx>
  • Date: Fri, 23 Feb 2007 10:13:56 -0500
  • Delivery-date: Fri, 23 Feb 2007 07:13:23 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdO73yfygbdSnxbR/2AnMRpBcbdNgAy2MewAXo9PloACVlAIAAAS21yAGSDywA=
  • Thread-topic: [Xen-devel] [PATCH][TOOLS] Reducing impactofdomainsave/restore/dump on Dom0

Take 3 -- I've moved the flushing/fadvise-ing code into a common routine
-- the only way I found to do this in line with other utilities was to
make it inline in xc_private.h (since this is the only file included in
both libxenctrl and libxenguest). The 'ifdef __linux__' stuff is now
confined to this routine which is better...

I've also left the fsync() in place -- I think it is necessary (and
certainly does no harm).


Reduce impact of saving/restoring/dumping large domains on Dom0 memory
usage by means of fadvise64() to tell the OS to discard the cache pages
used for the save/dump file.

Signed-off-by: Simon Graham <Simon.Graham@xxxxxxxxxxx>

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
> Sent: Wednesday, February 21, 2007 10:10 AM
> To: Graham, Simon; Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH][TOOLS] Reducing
> impactofdomainsave/restore/dump on Dom0
> On 21/2/07 15:06, "Graham, Simon" <Simon.Graham@xxxxxxxxxxx> wrote:
> > 2. sync-then-advise is only done at the end of writing a file to
> ensure
> > that all
> >    of the cached pages are discarded. Whilst writing the file, I
> > fadvise
> >    which triggers a write back and discards any clean pages up to
> > specified offset.
> >    This is indeed a performance thing -- fsyncing on every write
> makes
> > it very slow.
> Do you need the fsync at all? It's possible that the kernel will
> launder-then-discard the affected pages automatically, just from the
> fadvise() alone.
>  -- Keir

Attachment: xen-dom0-cache.patch
Description: xen-dom0-cache.patch

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