Re: [PATCH 2/2] hugetlb reservations: fix hugetlb MAP_PRIVATE reservations across vma splits

[Mel Gorman <mel@csn.ul.ie>]

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?

> <SNIP>

-- 
Mel Gorman

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