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    SubjectRe: [PATCH 1/4] workqueue:Fix unbound workqueue's node affinity detection
    On 12/16/2014 03:32 PM, Kamezawa Hiroyuki wrote:
    > (2014/12/16 14:30), Lai Jiangshan wrote:
    >> On 12/15/2014 07:14 PM, Kamezawa Hiroyuki wrote:
    >>> Unbound wq pool's node attribute is calculated at its allocation.
    >>> But it's now calculated based on possible cpu<->node information
    >>> which can be wrong after cpu hotplug/unplug.
    >>>
    >>> If wrong pool->node is set, following allocation error will happen.
    >>> ==
    >>> SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
    >>> cache: kmalloc-192, object size: 192, buffer size: 192, default order:
    >>> 1, min order: 0
    >>> node 0: slabs: 6172, objs: 259224, free: 245741
    >>> node 1: slabs: 3261, objs: 136962, free: 127656
    >>> ==
    >>>
    >>> This patch fixes the node detection by making use of online cpu info.
    >>> Unlike cpumask, the best node can be calculated by degree of overlap
    >>> between attr->cpumask and numanode->online_cpumask.
    >>> This change doesn't corrupt original purpose of the old calculation.
    >>>
    >>> Note: it's expected that this function is called as
    >>> pool_detect_best_node
    >>> get_unbound_pool
    >>> alloc_unbound_pwq
    >>> wq_update_unbound_numa
    >>> called at CPU_ONLINE/CPU_DOWN_PREPARE
    >>> and the latest online cpu info can be applied to a new wq pool,
    >>> which replaces old one.
    >>>
    >>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >>> ---
    >>> kernel/workqueue.c | 38 ++++++++++++++++++++++++++------------
    >>> 1 file changed, 26 insertions(+), 12 deletions(-)
    >>>
    >>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
    >>> index 09b685d..7809154 100644
    >>> --- a/kernel/workqueue.c
    >>> +++ b/kernel/workqueue.c
    >>> @@ -3440,6 +3440,31 @@ static void put_unbound_pool(struct worker_pool *pool)
    >>> }
    >>>
    >>> /**
    >>> + * pool_detect_best_node - detect a node which contains specified cpumask.
    >>> + * Should be called with wq_pool_mutex held.
    >>> + * Returns a online node where the most of given cpus are tied to.
    >>> + */
    >>> +static int pool_detect_best_node(const struct cpumask *cpumask)
    >>> +{
    >>> + int node, best, match, selected = NUMA_NO_NODE;
    >>> + static struct cpumask andmask; /* under wq_pool_mutex */
    >>> +
    >>> + if (!wq_numa_enabled ||
    >>> + cpumask_subset(cpu_online_mask, cpumask))
    >>> + goto out;
    >>> + best = 0;
    >>> + /* select a node which contains the most number of cpu */
    >>> + for_each_node_state(node, N_ONLINE) {
    >>> + cpumask_and(&andmask, cpumask, cpumask_of_node(node));
    >>> + match = cpumask_weight(&andmask);
    >>> + if (match > best)
    >>> + selected = best;
    >>> + }
    >>> +out:
    >>> + return selected;
    >>> +}
    >>
    >>
    >> This is a mixture of fix and development. Why not just keep the original calculation?
    >>
    > Just because wq_numa_possible_mask is broken,

    It is not broken if the bug is fixed.

    > it shouldn't be used if possible.
    > In this patch series, the mask is updated only when a node is coming up.
    > Is it better to clear it at node offline ?
    >
    >> if the mask cover multiple nodes, NUMA_NO_NODE is the best for pool->node
    >> after the pool was created. The memory allocation will select the best node
    >> for manage_workers(), from which CPU that the worker actually is running on.
    >>
    >
    > I'll drop this and try to keep original code as much as possible.
    >
    > Thanks,
    > -Kame
    >
    >
    > .
    >



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