RE: [Xen-devel] Re: Reducing impact of save/restore/dump on Dom0

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > Currently, save, restore and dump all used cached I/O in Dom0 to
> > write/read the file containing the memory image of the DomU - when
the
> > memory assigned to the DomU is greater than free memory in Dom0,
this
> > leads to severe memory thrashing and generally the Dom0 performance
goes
> > into the toilet.
> >
> > The 'classic' answer to avoiding this when writing very large files
is,
> > of course, to use non-cached I/O to manipulate the files -
> 
> Otherwise you can just use madvise()/fadvise() to tell the kernel
> to drop the old data [the later might need a fairly recent kernel
> to work]
> 
> It has the advantage that it doesn't need much other changes.

It's pretty easy for us to arrange that everything is page aligned. If
there was a measurable performance advantage using o_direct rather than
madvise/fadvise it probably makes sense to use it -- I can't see
o_direct going away any time soon.

Ian

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