Re: [PATCH] linux/balloon: prefer using pages from balloon in alloc_empty_pages_and_pagevec()

[Dave McCracken <dcm@mccr.org>]

On Wednesday 16 December 2009, Jan Beulich wrote:
> ... which seems to be broken at present anyway: The main loops in
> {alloc,free}_empty_pages_and_pagevec() both did not get their
> upper bound updated correctly (should be npages, but was left to
> be nr_pages), for alloc_empty_pages_and_pagevec() the wrong value
> is also being used to allocate pagevec[] (though I really think that this
> shouldn't allocate more than a nr_pages vector to avoid a rather large
> but unnecessary kmalloc() when nr_pages is small), and in its error
> path only a single page gets freed (rather than the whole
> balloon_order chunk).

You are correct.  The endpoint of the main loops should be npages, as should 
the variable used in the kmalloc().

I could only allocate the pagevec to be nr_pages and just fill it in with the 
partial order 9 page rather than rounding it up.  I'll ponder that.

I don't see anything wrong with the error path.  It correctly walks back down 
the pagevec and frees all the pages it's allocated so far.

Dave McCracken
Oracle Corp.