On Wed, Jun 08, 2011 at 09:42:19AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 8 Jun 2011 08:40:34 +0900
> <SNIP>
Missing a subject
>
> 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 and remove
> a code to get nid from page->flags. (Then, we'll use valid NID
> always.)
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> mm/page_cgroup.c | 41 +++++++++++++++++++++++++++++++++--------
> 1 file changed, 33 insertions(+), 8 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
> @@ -162,21 +162,25 @@ static void free_page_cgroup(void *addr)
> }
> #endif
>
> -static int __meminit init_section_page_cgroup(unsigned long pfn)
> +static int __meminit init_section_page_cgroup(unsigned long pfn, int nid)
> {
> struct page_cgroup *base, *pc;
> struct mem_section *section;
> unsigned long table_size;
> unsigned long nr;
> - int nid, index;
> + int index;
>
> + /*
> + * Even if passed 'pfn' is not aligned to section, we need to align
> + * it to section boundary because of SPARSEMEM pfn calculation.
> + */
> + pfn = ALIGN(pfn, PAGES_PER_SECTION);
> nr = pfn_to_section_nr(pfn);
This comment is a bit opaque and from the context of the patch,
it's hard to know why the alignment is necessary. At least move the
alignment to beside where section->page_cgroup is set because it'll
be easier to understand what is going on and why.
> section = __nr_to_section(nr);
>
> if (section->page_cgroup)
> return 0;
>
> - nid = page_to_nid(pfn_to_page(pfn));
> table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
> base = alloc_page_cgroup(table_size, nid);
>
> @@ -228,7 +232,7 @@ int __meminit online_page_cgroup(unsigne
> for (pfn = start; !fail && pfn < end; pfn += PAGES_PER_SECTION) {
> if (!pfn_present(pfn))
> continue;
> - fail = init_section_page_cgroup(pfn);
> + fail = init_section_page_cgroup(pfn, nid);
> }
> if (!fail)
> return 0;
> @@ -285,14 +289,35 @@ void __init page_cgroup_init(void)
> {
> unsigned long pfn;
> int fail = 0;
> + int node;
>
Very nit-picky but you sometimes use node and sometimes use nid.
Personally, nid is my preferred choice of name as its meaning is
unambigious.
> 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;
> + /*
> + * Because we cannot trust page->flags of page out of node
> + * boundary, we skip pfn < start_pfn.
> + */
> + for (pfn = start_pfn;
> + !fail && (pfn < end_pfn);
> + pfn = ALIGN(pfn + PAGES_PER_SECTION, PAGES_PER_SECTION)) {
> + if (!pfn_present(pfn))
> + continue;
Why did you not use pfn_valid()?
pfn_valid checks a section has SECTION_HAS_MEM_MAP
pfn_present checks a section has SECTION_MARKED_PRESENT
SECTION_MARKED_PRESENT does not necessarily mean mem_map has been
allocated although I admit that this is somewhat unlikely. I'm just
curious if you had a reason for avoiding pfn_valid()?
> + /*
> + * Nodes can be overlapped
> + * We know some arch can have nodes layout as
> + * -------------pfn-------------->
> + * N0 | N1 | N2 | N0 | N1 | N2 |.....
> + */
> + if (pfn_to_nid(pfn) != node)
> + continue;
> + fail = init_section_page_cgroup(pfn, node);
> + }
> }
> if (fail) {
> printk(KERN_CRIT "try 'cgroup_disable=memory' boot option\n");
>
FWIW, overall I think this is heading in the right direction.
Thanks.
--
Mel Gorman
SUSE Labs
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