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    SubjectRe: [PATCH v4 4/5] slub: Only IPI CPUs that have per cpu obj to flush
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    On Sun, Jan 1, 2012 at 2:41 PM, Avi Kivity <avi@redhat.com> wrote:
    > On 11/23/2011 08:23 AM, Pekka Enberg wrote:
    >> On Tue, 22 Nov 2011, Gilad Ben-Yossef wrote:
    >>> static void flush_all(struct kmem_cache *s)
    >>> {
    >>> -    on_each_cpu(flush_cpu_slab, s, 1);
    >>> +    cpumask_var_t cpus;
    >>> +    struct kmem_cache_cpu *c;
    >>> +    int cpu;
    >>> +
    >>> +    if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC))) {
    >>
    >> __GFP_NOWARN too maybe?
    >>
    >>> +        for_each_online_cpu(cpu) {
    >>> +            c = per_cpu_ptr(s->cpu_slab, cpu);
    >>> +            if (c->page)
    >>> +                cpumask_set_cpu(cpu, cpus);
    >>> +        }
    >>> +        on_each_cpu_mask(cpus, flush_cpu_slab, s, 1);
    >>> +        free_cpumask_var(cpus);
    >>> +    } else
    >>> +        on_each_cpu(flush_cpu_slab, s, 1);
    >>> }
    >>
    >
    > Since this seems to be a common pattern, how about:
    >
    >   zalloc_cpumask_var_or_all_online_cpus(&cpus, GFTP_ATOMIC);
    >   ...
    >   free_cpumask_var(cpus);
    >
    > The long-named function at the top of the block either returns a newly
    > allocated zeroed cpumask, or a static cpumask with all online cpus set.
    > The code in the middle is only allowed to set bits in the cpumask
    > (should be the common usage).  free_cpumask_var() needs to check whether
    > the freed object is the static variable.

    Thanks for the feedback and advice! I totally agree the repeating
    pattern needs abstracting.

    I ended up chosing to try a different abstraction though - basically a wrapper
    on_each_cpu_cond that gets a predicate function to run per CPU to
    build the mask
    to send the IPI to. It seems cleaner to me not having to mess with
    free_cpumask_var
    and it abstracts more of the general pattern.

    I intend to run the new code through some more testing tomorrow and send out V5
    of the patch set. I'd be delighted if you can have a look through it then.

    Thanks!
    Gilad

    --
    Gilad Ben-Yossef
    Chief Coffee Drinker
    gilad@benyossef.com
    Israel Cell: +972-52-8260388
    US Cell: +1-973-8260388
    http://benyossef.com

    "Unfortunately, cache misses are an equal opportunity pain provider."
    -- Mike Galbraith, LKML
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