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    SubjectRe: [PATCH 05/30] mm: slb: add knowledge of reserve pages
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    On Tue, 2008-08-12 at 15:35 +1000, Neil Brown wrote:
    > On Thursday July 24, a.p.zijlstra@chello.nl wrote:
    > > Restrict objects from reserve slabs (ALLOC_NO_WATERMARKS) to allocation
    > > contexts that are entitled to it. This is done to ensure reserve pages don't
    > > leak out and get consumed.
    >
    > This looks good (we are still missing slob though, aren't we :-( )

    I actually have that now, just needs some testing..

    > > @@ -1526,7 +1540,7 @@ load_freelist:
    > > object = c->page->freelist;
    > > if (unlikely(!object))
    > > goto another_slab;
    > > - if (unlikely(SLABDEBUG && PageSlubDebug(c->page)))
    > > + if (unlikely(PageSlubDebug(c->page) || c->reserve))
    > > goto debug;
    >
    > This looks suspiciously like debugging code that you have left in.
    > Is it??

    Its not, we need to force slub into the debug slow path when we have a
    reserve page, otherwise we cannot do the permission check on each
    allocation.

    > > @@ -265,7 +267,8 @@ struct array_cache {
    > > unsigned int avail;
    > > unsigned int limit;
    > > unsigned int batchcount;
    > > - unsigned int touched;
    > > + unsigned int touched:1,
    > > + reserve:1;
    >
    > This sort of thing always worries me.
    > It is a per-cpu data structure so you won't get SMP races corrupting
    > fields. But you do get read-modify-write in place of simple updates.
    > I guess it's not a problem.. But it worries me :-)

    Right,.. do people prefer I just add another int?



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