Re: [PATCH 3/3] hugetlb: fix absurd HugePages_Rsvd

[David Gibson <david@gibson.dropbear.id.au>]

On Wed, Oct 25, 2006 at 08:23:13AM +0300, Mika Penttila wrote:
> Hugh Dickins wrote:
> >If you truncated an mmap'ed hugetlbfs file, then faulted on the truncated
> >area, /proc/meminfo's HugePages_Rsvd wrapped hugely "negative".  Reinstate
> >my preliminary i_size check before attempting to allocate the page (though
> >this only fixes the most obvious case: more work will be needed here).
> >
> >Signed-off-by: Hugh Dickins <hugh@veritas.com>
> >___
> >
> >This is not a complete solution (what if hugetlb_no_page is actually
> >racing with truncate_hugepages?), and there are several other accounting
> >anomalies in here (private versus shared pages, hugetlbfs quota handling);
> >but those all need more thought.  It'll probably make sense to use i_mutex
> >instead of hugetlb_instantiation_mutex, so locking out truncation and 
> >mmap.
> >
> > mm/hugetlb.c |    3 +++
> > 1 file changed, 3 insertions(+)
> >
> >--- 2.6.19-rc3/mm/hugetlb.c	2006-10-24 04:34:37.000000000 +0100
> >+++ linux/mm/hugetlb.c	2006-10-24 16:23:17.000000000 +0100
> >@@ -478,6 +478,9 @@ int hugetlb_no_page(struct mm_struct *mm
> > retry:
> > 	page = find_lock_page(mapping, idx);
> > 	if (!page) {
> >+		size = i_size_read(mapping->host) >> HPAGE_SHIFT;
> >+		if (idx >= size)
> >+			goto out;
> > 		if (hugetlb_get_quota(mapping))
> > 			goto out;
> > 		page = alloc_huge_page(vma, address);
> >
> Shouldn't it be something like following ?
> 
> size = (i_size_read(mapping->host) + HPAGE_SIZE - 1) >> HPAGE_SHIFT;
> 
> 
> 
> If so this was wrong in the original code also.

In theory, yes, but AFAIK there is no way to get an i_size on a
hugetlbfs file which is not a multiple of HPAGE_SIZE.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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