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    SubjectRe: [PATCH] mm: get_nid_for_pfn() returns int
    On Mon, Jan 26, 2009 at 10:33:50PM -0800, Andrew Morton wrote:
    > On Mon, 19 Jan 2009 09:59:19 -0800 Gary Hade <garyhade@us.ibm.com> wrote:
    >
    > > On Sun, Jan 18, 2009 at 11:36:28PM +0100, Roel Kluin wrote:
    > > > get_nid_for_pfn() returns int
    > > >
    > > > Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
    > > > ---
    > > > vi drivers/base/node.c +256
    > > > static int get_nid_for_pfn(unsigned long pfn)
    > > >
    > > > diff --git a/drivers/base/node.c b/drivers/base/node.c
    > > > index 43fa90b..f8f578a 100644
    > > > --- a/drivers/base/node.c
    > > > +++ b/drivers/base/node.c
    > > > @@ -303,7 +303,7 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk)
    > > > sect_start_pfn = section_nr_to_pfn(mem_blk->phys_index);
    > > > sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1;
    > > > for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
    > > > - unsigned int nid;
    > > > + int nid;
    > > >
    > > > nid = get_nid_for_pfn(pfn);
    > > > if (nid < 0)
    > >
    > > My mistake. Good catch.
    > >
    >
    > Presumably the (nid < 0) case has never happened.

    We do know that it is happening on one system while creating
    a symlink for a memory section so it should also happen on
    the same system if unregister_mem_sect_under_nodes() were
    called to remove the same symlink.

    The test was actually added in response to a problem with an
    earlier version reported by Yasunori Goto where one or more
    of the leading pages of a memory section on the 2nd node of
    one of his systems was uninitialized because I believe they
    coincided with a memory hole. The earlier version did not
    ignore uninitialized pages and determined the nid by considering
    only the 1st page of each memory section. This caused the
    symlink to the 1st memory section on the 2nd node to be
    incorrectly created in /sys/devices/system/node/node0 instead
    of /sys/devices/system/node/node1. The problem was fixed by
    adding the test to skip over uninitialized pages.

    I suspect we have not seen any reports of the non-removal
    of a symlink due to the incorrect declaration of the nid
    variable in unregister_mem_sect_under_nodes() because
    - systems where a memory section could have an uninitialized
    range of leading pages are probably rare.
    - memory remove is probably not done very frequently on the
    systems that are capable of demonstrating the problem.
    - lingering symlink(s) that should have been removed may
    have simply gone unnoticed.
    >
    > Should we retain the test?

    Yes.

    >
    > Is silently skipping the node in that case desirable behaviour?

    It actually silently skips pages (not nodes) in it's quest
    for valid nids for all the nodes that the memory section scans.
    This is definitely desirable.

    I hope this answers your questions.

    Thanks,
    Gary

    --
    Gary Hade
    System x Enablement
    IBM Linux Technology Center
    503-578-4503 IBM T/L: 775-4503
    garyhade@us.ibm.com
    http://www.ibm.com/linux/ltc



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