Xen devel - Feb 2007 - RE: [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).

Simon

-----------------------------------
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@stratus.com>

> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-
> bounces@lists.xensource.com] On Behalf Of Keir Fraser
> Sent: Wednesday, February 21, 2007 10:10 AM
> To: Graham, Simon; Keir Fraser; xen-devel@lists.xensource.com
> Subject: Re: [Xen-devel] [PATCH][TOOLS] Reducing
> impactofdomainsave/restore/dump on Dom0
> 
> On 21/2/07 15:06, "Graham, Simon"
<Simon.Graham@stratus.com> 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
only
> > fadvise
> >    which triggers a write back and discards any clean pages up to
the
> > 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

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On 23/2/07 15:13, "Graham, Simon" <Simon.Graham@stratus.com>
wrote:
> 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).
Looks better. What is the -D_GNU_SOURCE for? It should probably at least be
limited to CFLAGS-$(CONFIG_Linux). And is it really needed in
xcutil/Makefile as well: if it''s needed at all it should suffice to use
it
when building the library that xcutil links against I would have thought?

 -- Keir


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