RE: [PATCH 2/3 htlb-fault] Demand faulting for hugetlb

[Adam Litke <agl@us.ibm.com>]

On Wed, 2005-09-07 at 10:33 +0800, Zhang, Yanmin wrote:
> >>-----Original Message-----
> >>From: linux-kernel-owner@vger.kernel.org
> >>[mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Adam Litke
> >>Sent: Wednesday, September 07, 2005 5:59 AM
> >>To: linux-kernel@vger.kernel.org
> >>Cc: ADAM G. LITKE [imap]
> >>Subject: Re: [PATCH 2/3 htlb-fault] Demand faulting for hugetlb
> 
> >>+retry:
> >>+	page = find_get_page(mapping, idx);
> >>+	if (!page) {
> >>+		/* charge the fs quota first */
> >>+		if (hugetlb_get_quota(mapping)) {
> >>+			ret = VM_FAULT_SIGBUS;
> >>+			goto out;
> >>+		}
> >>+		page = alloc_huge_page();
> >>+		if (!page) {
> >>+			hugetlb_put_quota(mapping);
> >>+			ret = VM_FAULT_SIGBUS;
> >>+			goto out;
> >>+		}
> >>+		if (add_to_page_cache(page, mapping, idx, GFP_ATOMIC)) {
> 
> Here you lost hugetlb_put_quota(mapping);

Whoops, thanks for catching that.

> >>+			put_page(page);
> >>+			goto retry;
> >>+		}
> >>+		unlock_page(page);
> 
> As for regular pages, kernel is used to unlock mm-> page_table_lock
> before find_get_page and relock it before setting pte. Why isn't the
> style followed by huge page fault?

As far as I can tell, we should be able to do that for large pages as
well.  I'll give it a spin.

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center