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    SubjectRe: [PATCH] cpuset: fix allocating page cache/slab object on the unallowed node when memory spread is set
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    On Thursday 12 February 2009 19:27:16 Miao Xie wrote:
    > on 2009-2-12 9:55 Nick Piggin wrote:
    > > On Thursday 12 February 2009 12:19:11 Paul Menage wrote:
    > >> On Wed, Feb 11, 2009 at 4:54 PM, Nick Piggin <nickpiggin@yahoo.com.au>
    > >
    > > wrote:
    > >>> It would be possible, depending on timing, for the allocating thread to
    > >>> see either pre or post mems_allowed even if access was fully locked.
    > >>
    > >> Right - seeing either the pre set or the post set is fine.
    > >>
    > >>> The only difference is that a partially changed mems_allowed could be
    > >>> seen. But what does this really mean? Some combination of the new and
    > >>> the old nodes. I don't think this is too much of a problem.
    > >>
    > >> But if the old and new nodes are disjoint, that could lead to seeing no
    > >> nodes.
    > >
    > > Well we could structure updates as setting all new allowed nodes,
    > > then clearing newly disallowed ones.
    >
    > But it still has the other problem. such as:
    > Task1 Task2
    > get_page_from_freelist() while(1) {
    > {
    > for_each_zone_zonelist_nodemask() {
    > change Task1's mems_allowed
    > if (!cpuset_zone_allowed_softwall())
    > goto try_next_zone;
    > try_next_zone:
    > ...
    > }
    > } }
    >
    > In the extreme case, Task1 will be completely unable to allocate memory
    > at worst. At least, it will lead to the delay of allocate pages. Though
    > the probability of this case is very low, we have to take into account.

    Hmm, but a task with that permission could kill task1 in a number
    of ways. Is it really worth worrying about?



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