Messages in this thread | | | Date | Sun, 13 Nov 2011 16:57:36 +0200 | Subject | Re: [PATCH v3 4/5] slub: Only IPI CPUs that have per cpu obj to flush | From | Gilad Ben-Yossef <> |
| |
On Sun, Nov 13, 2011 at 2:20 PM, Hillf Danton <dhillf@gmail.com> wrote: > > On Sun, Nov 13, 2011 at 6:17 PM, Gilad Ben-Yossef <gilad@benyossef.com> wrote: > ... > > > diff --git a/mm/slub.c b/mm/slub.c > > index 7d2a996..caf4b3a 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -2006,7 +2006,20 @@ static void flush_cpu_slab(void *d) > > > > 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))) { > > Perhaps, the technique of local_cpu_mask defined in kernel/sched_rt.c > could be used to replace the above atomic allocation. >
Thank you for taking the time to review my patch :-)
That is indeed the direction I went with inthe previous iteration of this patch, with the small change that because of observing that the allocation will only actually occurs for CPUMASK_OFFSTACK=y which by definition are systems with lots and lots of CPUs and, it is actually better to allocate the cpumask per kmem_cache rather then per CPU, since on system where it matters we are bound to have more CPUs (e.g. 4096) then kmem_caches (~160). See https://lkml.org/lkml/2011/10/23/151.
I then went a head and further optimized the code to only incur the memory overhead of allocating those cpumasks for CPUMASK_OFFSTACK=y systems. See https://lkml.org/lkml/2011/10/23/152.
As you can see from the discussion that evolved, there seems to be an agreement that the code complexity overhead involved is simply not worth it for what is, unlike sched_rt, a rather esoteric case and one where allocation failure is easily dealt with.
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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |