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    SubjectRe: Why kmem_cache_free occupy CPU for more than 10 seconds?
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    On Thu, 2007-04-12 at 00:55 -0700, Andrew Morton wrote:
    > On Thu, 12 Apr 2007 09:39:25 +0200 Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    >
    > > On Wed, 2007-04-11 at 15:30 -0700, Andrew Morton wrote:
    > >
    > > > There used to be a cond_resched() in invalidate_mapping_pages() which would
    > > > have prevented this, but I rudely removed it to support
    > > > /proc/sys/vm/drop_caches (which needs to call invalidate_inode_pages()
    > > > under spinlock).
    > > >
    > > > We could resurrect that cond_resched() by passing in some flag, I guess.
    > > > Or change the code to poke the softlockup detector. The former would be
    > > > better.
    > >
    > > cond_resched() is conditional on __resched_legal(0)
    >
    > What's __resched_legal()?

    Hmm, I was looking at the RHEL-5 sources, it seems this function was
    removed later (commmit 9414232fa0cc28e2f51b8c76d260f2748f7953fc).

    > > which should take
    > > care of being called under a spinlock.
    >
    > We only increment preempt_count() in spin_lock() if CONFIG_PREEMPT.

    Right, ok, that makes the whole thing fall apart indeed.

    > > Index: linux-2.6-mm/mm/truncate.c
    > > ===================================================================
    > > --- linux-2.6-mm.orig/mm/truncate.c
    > > +++ linux-2.6-mm/mm/truncate.c
    > > @@ -292,6 +292,8 @@ unsigned long invalidate_mapping_pages(s
    > > pgoff_t index;
    > > int lock_failed;
    > >
    > > + cond_resched();
    > > +
    > > lock_failed = TestSetPageLocked(page);
    >
    > Is deadlocky on the drop_caches path and if CONFIG_PREEMPT we'll get
    > scheduling-in-spinlock warnings.

    *nod*

    > For the blkdev_close() path the change is unneeded if CONFIG_PREEMPT and
    > will fix things if !CONFIG_PREEMPT.
    >
    > We can presumably just remove the invalidate_mapping_pages() call from the
    > kill_bdev() path (at least) - kill_bdev()'s truncate_inode_pages() will do
    > the same thing.

    Certainly looks that way, I'll see if I can spot a hole in that.

    > It might be time to remove that unused-for-six-years destroy_dirty_buffers
    > too.

    ok.

    -
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