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    SubjectRe: Deadlock possibly caused by too_many_isolated.
    On Wed, Sep 15, 2010 at 10:37:35AM +0800, Wu Fengguang wrote:
    > On Wed, Sep 15, 2010 at 10:23:34AM +0800, Neil Brown wrote:
    > > On Tue, 14 Sep 2010 20:30:18 -0400
    > > Rik van Riel <riel@redhat.com> wrote:
    > >
    > > > On 09/14/2010 07:11 PM, Neil Brown wrote:
    > > >
    > > > > Index: linux-2.6.32-SLE11-SP1/mm/vmscan.c
    > > > > ===================================================================
    > > > > --- linux-2.6.32-SLE11-SP1.orig/mm/vmscan.c 2010-09-15 08:37:32.000000000 +1000
    > > > > +++ linux-2.6.32-SLE11-SP1/mm/vmscan.c 2010-09-15 08:38:57.000000000 +1000
    > > > > @@ -1106,6 +1106,11 @@ static unsigned long shrink_inactive_lis
    > > > > /* We are about to die and free our memory. Return now. */
    > > > > if (fatal_signal_pending(current))
    > > > > return SWAP_CLUSTER_MAX;
    > > > > + if (!(sc->gfp_mask& __GFP_IO))
    > > > > + /* Not allowed to do IO, so mustn't wait
    > > > > + * on processes that might try to
    > > > > + */
    > > > > + return SWAP_CLUSTER_MAX;
    > > > > }
    > > > >
    > > > > /*
    > > >
    > > > Close. We must also be sure that processes without __GFP_FS
    > > > set in their gfp_mask do not wait on processes that do have
    > > > __GFP_FS set.
    > > >
    > > > Considering how many times we've run into a bug like this,
    > > > I'm kicking myself for not having thought of it :(
    > > >
    > >
    > > So maybe this? I've added the test for __GFP_FS, and moved the test before
    > > the congestion_wait on the basis that we really want to get back up the stack
    > > and try the mempool ASAP.
    >
    > The patch may well fail the !__GFP_IO page allocation and then
    > quickly exhaust the mempool.
    >
    > Another approach may to let too_many_isolated() use much higher
    > thresholds for !__GFP_IO/FS and lower ones for __GFP_IO/FS. ie. to
    > allow at least nr2 NOIO/FS tasks to be blocked independent of the
    > IO/FS ones. Since NOIO vmscans typically completes fast, it will then
    > very hard to accumulate enough NOIO processes to be actually blocked.
    >
    >
    > IO/FS tasks NOIO/FS tasks full
    > block here block here LRU size
    > |-----------------|--------------------------|-----------------------|
    > | nr1 | nr2 |

    How about this fix? We may need very high threshold for NOIO/NOFS to
    prevent possible regressions.

    Thanks,
    Fengguang
    ---

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 225a759..5e116cd 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -1135,6 +1135,7 @@ static int too_many_isolated(struct zone *zone, int file,
    struct scan_control *sc)
    {
    unsigned long inactive, isolated;
    + int ratio;

    if (current_is_kswapd())
    return 0;
    @@ -1150,7 +1151,9 @@ static int too_many_isolated(struct zone *zone, int file,
    isolated = zone_page_state(zone, NR_ISOLATED_ANON);
    }

    - return isolated > inactive;
    + ratio = sc->gfp_mask & (__GFP_FS|__GFP_IO) ? 1 : 8;
    +
    + return isolated > inactive * ratio;
    }

    /*

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