linux-kernel - Re: Regression - locking (all from 2.6.28)

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Date:	Fri, 06 Mar 2009 16:40:16 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	jan sonnek <ha2nny@...il.com>, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Whitcroft <apw@...dowen.org>
Subject: Re: Regression - locking (all from 2.6.28)

On Wed, 2009-03-04 at 16:54 -0800, Dave Hansen wrote:
> On Tue, 2009-03-03 at 15:01 +0000, Catalin Marinas wrote:
> > > +     /* mem_map scanning */
> > > +     for_each_online_node(i) {
> > > +             struct page *page, *end;
> > > +
> > > +             page = NODE_MEM_MAP(i);
> > > +             end  = page + NODE_DATA(i)->node_spanned_pages;
> > > +
> > > +             scan_block(page, end, NULL);
> > > +     }
[...]
> One completely unoptimized thing you can do which will scan a 'struct
> page' at a time is this:
> 
> 	for_each_online_node(i) {
> 		unsigned long pfn;
> 		for (pfn = node_start_pfn(i); pfn < node_end_pfn(i); pfn++) {
> 			struct page *page;
> 			if (!pfn_valid(pfn))
> 				continue;
> 			page = pfn_to_page(pfn);
> 			scan_block(page, page+1, NULL);
> 		}
> 	}

It seems that node_start_pfn() isn't present on all the architectures. I
ended up with something like below:

+	/* struct page scanning for each node */
+	for_each_online_node(i) {
+		pg_data_t *pgdat = NODE_DATA(i);
+		unsigned long start_pfn = pgdat->node_start_pfn;
+		unsigned long end_pfn = start_pfn +
+			pgdat->node_spanned_pages - 1;
+		unsigned long pfn;
+
+		for (pfn = start_pfn; pfn < end_pfn; pfn++) {
+			struct page *page;
+
+			if (!pfn_valid(pfn))
+				continue;
+			page = pfn_to_page(pfn);
+			/* only scan if page is in use */
+			if (page_count(page) == 0)
+				continue;
+			scan_block(page, page + 1, NULL);
+		}
+	}

Are the pgdat->node_start_pfn and pgdat->node_spanned_pages always
valid? Thanks.

-- 
Catalin

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