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Re: [Xen-devel] [PATCH] tools: fix build after recent xenpaging changes

On Fri, 2011-06-24 at 15:35 +0100, Olaf Hering wrote:
> On Fri, Jun 24, Ian Campbell wrote:
> > > The break exits the for() loop, not the while(1). In the next iteration
> > > page 1 may still be in paging->bitmap and tried again.
> > 
> > I'd missed the interrupted -> 1 in the while loop. I presume there is
> > some other exit condition which triggers once everything has been paged
> > back in and actually causes the daemon to exit?
> If the for() loop found nothing, then this triggers:
> 775             /* If no more pages to process, exit loop */
> 776             if ( i == paging->domain_info->max_pages )
> 777                 break;

Oh yes.

It's a bit counter intuitive to have a for loop which only processes the
first thing it finds and then relying on going round another outer loop
to pickup the second etc. It's at least O(N^2), isn't it?

Why not 
        count = 0;
        for ( i = 0; i < paging->domain_info->max_pages; i++ )
                if ( test_bit(i, paging->bitmap) )
            /* If no more pages to process, exit loop */
            if ( !count )

That will at least process as many pages as it can on each iteration
through the outer loop. Although it will most likely exacerbate the
locking issue I pointed to earlier.


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