On Tue, Jun 07, 2011 at 06:33:02PM +0900, KAMEZAWA Hiroyuki wrote:
> On Tue, 7 Jun 2011 10:09:00 +0100
> Mel Gorman <mgorman@xxxxxxx> wrote:
>
> > I should have said "nodes" even though the end result is the same. The
> > problem at the moment is cgroup initialisation is checking PFNs outside
> > node boundaries. It should be ensuring that the start and end PFNs it
> > uses are within boundaries.
> >
> Maybe you like this kind of fix. Yes, this can fix the problem on bugzilla.
> My concern is this will not work for ARM.
>
> This patch (and all other patch) works on my test host.
> ==
> make sparsemem's page_cgroup_init to be node aware.
>
> With sparsemem, page_cgroup_init scans pfn from 0 to max_pfn.
> But this may scan a pfn which is not on any node and can access
> memmap which is not initialized.
>
> This makes page_cgroup_init() for SPARSEMEM node aware.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> mm/page_cgroup.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> Index: linux-3.0-rc1/mm/page_cgroup.c
> ===================================================================
> --- linux-3.0-rc1.orig/mm/page_cgroup.c
> +++ linux-3.0-rc1/mm/page_cgroup.c
> @@ -285,14 +285,32 @@ void __init page_cgroup_init(void)
> {
> unsigned long pfn;
> int fail = 0;
> + int node;
>
> if (mem_cgroup_disabled())
> return;
>
> - for (pfn = 0; !fail && pfn < max_pfn; pfn += PAGES_PER_SECTION) {
> - if (!pfn_present(pfn))
> - continue;
> - fail = init_section_page_cgroup(pfn);
> + for_each_node_state(node, N_HIGH_MEMORY) {
> + unsigned long start_pfn, end_pfn;
> +
> + start_pfn = NODE_DATA(node)->node_start_pfn;
> + end_pfn = start_pfn + NODE_DATA(node)->node_spanned_pages;
> + /*
> + * This calculation makes sure that this nid detection for
> + * section can work even if node->start_pfn is not aligned to
> + * section. For sections on not-node-boundary, we see head
> + * page of sections.
> + */
> + for (pfn = start_pfn;
> + !fail & (pfn < end_pfn);
&& instead of & there?
> + pfn = ALIGN(pfn + PAGES_PER_SECTION, PAGES_PER_SECTION)) {
> + if (!pfn_present(pfn))
> + continue;
> + /* Nodes can be overlapped */
> + if (pfn_to_nid(pfn) != node)
> + continue;
> + fail = init_section_page_cgroup(pfn);
> + }
So this is finding the first valid PFN in a node. Even the
overlapping problem should not be an issue here as unless node memory
initialisation is overwriting flags belonging to other nodes. The
paranoia does not hurt.
I also don't think the ARM punching holes in the memmap is a problem
because we'd at least expect the start of the node to be valid.
--
Mel Gorman
SUSE Labs
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