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    SubjectRe: [PATCH] online CPU before memory failed in pcpu_alloc_pages()
    On Tue, 18 May 2010 14:17:22 +0800
    minskey guo <chaohong_guo@linux.intel.com> wrote:

    > From: minskey guo <chaohong.guo@intel.com>
    >
    > The operation of "enable CPU to online before memory within a node"
    > fails in some case according to Prarit. The warnings as follows:
    >
    > Pid: 7440, comm: bash Not tainted 2.6.32 #2
    > Call Trace:
    > [<ffffffff81155985>] pcpu_alloc+0xa05/0xa70
    > [<ffffffff81155a20>] __alloc_percpu+0x10/0x20
    > [<ffffffff81089605>] __create_workqueue_key+0x75/0x280
    > [<ffffffff8110e050>] ? __build_all_zonelists+0x0/0x5d0
    > [<ffffffff810c1eba>] stop_machine_create+0x3a/0xb0
    > [<ffffffff810c1f57>] stop_machine+0x27/0x60
    > [<ffffffff8110f1a0>] build_all_zonelists+0xd0/0x2b0
    > [<ffffffff814c1d12>] cpu_up+0xb3/0xe3
    > [<ffffffff814b3c40>] store_online+0x70/0xa0
    > [<ffffffff81326100>] sysdev_store+0x20/0x30
    > [<ffffffff811d29a5>] sysfs_write_file+0xe5/0x170
    > [<ffffffff81163d28>] vfs_write+0xb8/0x1a0
    > [<ffffffff810cfd22>] ? audit_syscall_entry+0x252/0x280
    > [<ffffffff81164761>] sys_write+0x51/0x90
    > [<ffffffff81013132>] system_call_fastpath+0x16/0x1b
    > Built 4 zonelists in Zone order, mobility grouping on. Total pages: 12331603
    > PERCPU: allocation failed, size=128 align=64, failed to populate
    >
    > With "enable CPU to online before memory" patch, when the 1st CPU of
    > an offlined node is being onlined, we build zonelists for that node.
    > If per-cpu area needs to be extended during zonelists building period,
    > alloc_pages_node() will be called. The routine alloc_pages_node() fails
    > on the node in-onlining because the node doesn't have zonelists created
    > yet.
    >
    > To fix this issue, we try to alloc memory from current node.

    How serious is this issue? Just a warning? Dead box?

    Because if we want to port this fix into 2.6.34.x, we have a little
    problem.


    > --- a/mm/percpu.c
    > +++ b/mm/percpu.c
    > @@ -714,13 +714,29 @@ static int pcpu_alloc_pages(struct pcpu_chunk *chunk,

    In linux-next, Tejun has gone and moved pcpu_alloc_pages() into the new
    mm/percpu-vm.c. So either

    a) the -stable guys will need to patch a different file or

    b) we apply this fix first and muck up Tejun's tree or

    c) the bug isn't very serious so none of this applies.

    > {
    > const gfp_t gfp = GFP_KERNEL | __GFP_HIGHMEM | __GFP_COLD;
    > unsigned int cpu;
    > + int nid;
    > int i;
    >
    > for_each_possible_cpu(cpu) {
    > for (i = page_start; i < page_end; i++) {
    > struct page **pagep = &pages[pcpu_page_idx(cpu, i)];
    >
    > - *pagep = alloc_pages_node(cpu_to_node(cpu), gfp, 0);
    > + nid = cpu_to_node(cpu);
    > +
    > + /*
    > + * It is allowable to online a CPU within a NUMA
    > + * node which doesn't have onlined local memory.
    > + * In this case, we need to create zonelists for
    > + * that node when cpu is being onlined. If per-cpu
    > + * area needs to be extended at the exact time when
    > + * zonelists of that node is being created, we alloc
    > + * memory from current node.
    > + */
    > + if ((nid == -1) ||
    > + !(node_zonelist(nid, GFP_KERNEL)->_zonerefs->zone))
    > + nid = numa_node_id();
    > +
    > + *pagep = alloc_pages_node(nid, gfp, 0);
    > if (!*pagep) {
    > pcpu_free_pages(chunk, pages, populated,
    > page_start, page_end);



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