Re: [Libhugetlbfs-devel] [PATCH 3/5] hugetlb: Try to grow hugetlb pool for MAP_PRIVATE mappings

[Dave Hansen <haveblue@us.ibm.com>]

On Thu, 2007-09-13 at 10:59 -0700, Adam Litke wrote:
> +static int within_locked_vm_limits(long hpage_delta)
> +{
> +	unsigned long locked_pages, locked_pages_limit;
> +
> +	/* Check locked page limits */
> +	locked_pages = current->mm->locked_vm;
> +	locked_pages += hpage_delta * (HPAGE_SIZE >> PAGE_SHIFT);
> +	locked_pages_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
> +	locked_pages_limit >>= PAGE_SHIFT;
> +
> +	/* Return 0 if we would exceed locked_vm limits */
> +	if (locked_pages > locked_pages_limit)
> +		return 0;
> +
> +	/* Nice, we're within limits */
> +	return 1;
> +}
> +
> +static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
> +						unsigned long address)
> +{
> +	struct page *page;
> +
> +	/* Check we remain within limits if 1 huge page is allocated */
> +	if (!within_locked_vm_limits(1))
> +		return NULL;
> +
> +	page = alloc_pages(htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
...

Is there locking around this operation?  Or, is there a way that a
process could do this concurrently in two different threads, both appear
to be within within_locked_vm_limits(), and both succeed to allocate
when doing so actually takes them over the limit?

-- Dave

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