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SubjectRe: [PATCH 2/2] hugetlb reservations: fix hugetlb MAP_PRIVATE reservations across vma splits
On Mon, Jun 23, 2008 at 09:00:48AM +0100, Mel Gorman wrote:
> Typical. I spotted this after I pushed send.....
>
> > <SNIP>
>
> > @@ -266,14 +326,19 @@ static void decrement_hugepage_resv_vma(struct hstate *h,
> > * private mappings.
> > */
> > if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
> > - unsigned long flags, reserve;
> > + unsigned long idx = vma_pagecache_offset(h,
> > + vma, address);
> > + struct resv_map *reservations = vma_resv_map(vma);
> > +
> > h->resv_huge_pages--;
> > - flags = (unsigned long)vma->vm_private_data &
> > - HPAGE_RESV_MASK;
> > - reserve = (unsigned long)vma->vm_private_data - 1;
> > - vma->vm_private_data = (void *)(reserve | flags);
> > +
> > + /* Mark this page used in the map. */
> > + if (region_chg(&reservations->regions, idx, idx + 1) < 0)
> > + return -1;
> > + region_add(&reservations->regions, idx, idx + 1);
> > }
>
> decrement_hugepage_resv_vma() is called with hugetlb_lock held and region_chg
> calls kmalloc(GFP_KERNEL). Hence it's possible we would sleep with that
> spinlock held which is a bit uncool. The allocation needs to happen outside
> the lock. Right?

Yes, good spot. Luckily this pair of calls can be separated, as the
first is a prepare and the second a commit. So I can trivially pull
the allocation outside the lock.

Had a quick go at this and it looks like I can move both out of the lock
to a much more logical spot and clean the patch up significantly. Will
fold in your other comments and post up a V2 once it has been tested.

Thanks.

-apw


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