Re: [v4][PATCH 2/2] fix large pages in pagemap

[Matt Mackall <mpm@selenic.com>]

[adding Hugh to the cc:]

On Wed, 2008-06-11 at 12:37 -0700, Andrew Morton wrote:
> On Wed, 11 Jun 2008 11:02:31 -0700
> Dave Hansen <dave@linux.vnet.ibm.com> wrote:
> 
> > 
> > We were walking right into huge page areas in the pagemap
> > walker, and calling the pmds pmd_bad() and clearing them.
> > 
> > That leaked huge pages.  Bad.
> > 
> > This patch at least works around that for now.  It ignores
> > huge pages in the pagemap walker for the time being, and
> > won't leak those pages.
> > 
> 
> I don't get it.   Why can't we just stick a
> 
> 	if (pmd_huge(pmd))
> 		continue;
> 
> into pagemap_pte_range()?  Or something like that.

That's certainly what you'd hope to be able to do, yes.

If I recall the earlier discussion, some arches with huge pages can only
identify them via a VMA. Obviously, any arch with hardware that walks
our pagetables directly must be able to identify huge pages directly
from those tables, but I think PPC and a couple others that don't have
hardware TLB fill fail to store such a bit in the tables at all.

-- 
Mathematics is the supreme nostalgia of our time.

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