Re: [Xen-devel] [PATCH][TOOLS] Reducing impact ofdomainsave/restore/dump on Dom0

[Robert Read <rread@xxxxxxxxxxxxx>]

Hi,

I also read somewhere (either the man page or in the code) that the  
sync is necessary for exactly these reasons.
robert


On Feb 21, 2007, at 07:22, Graham, Simon wrote:

> > 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.
> To be honest, I'm not completely sure; the implementation of the  
> fadvise
> call triggers a write back and then explicitely discards any clean  
> pages
> -- I don't _think_ it will discard clean pages once the write back
> completes (but it's not entirely clear to me how much of the write  
> back
> is done synchronously).
>
> However, it definitely makes a perf difference if you explicitely  
> fsync
> before each call to fadvise -- therefore I believe that the fadvise  
> call
> is definitely not cleaning all the pages inline (which would be
> equivalent to the fsync()).
>
> So -- my belief is that without the fsync, there will be some (clean)
> pages for the file still in the cache when this is done; my goal  
> was to
> remove ALL the pages, but perhaps leaving a few lying around is OK..
>
> /simgr
>
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