On Wed, Feb 08, 2017 at 01:03:55PM +0100, Michal Hocko wrote:
> > I don't object to it being actually moved. I have a slight concern that
> > it could somehow starve a vmstat update while frequent drains happen
> > during reclaim though which potentially compounds the problem. It could
> > be offset by a variety of other factors but if it ever is an issue,
> > it'll show up and the paths that really matter check the vmstats
> > directly instead of waiting for an update.
>
> vmstat updates can tolared delays, that's we we are using deferable
> scheduling in the first place so I am not really worried about that. Any
> user which needs a better precision should use *_snapshot API.
>
Agreed, we already had cases where deferred vmstat updates had problems
and were resolved by using _snapshot. It's a slight concern only and I'd
be surprised if the _snapshot usage didn't cover it.
> > The altering of the return value in setup_vmstat was mildly surprising as
> > it increases the severity of registering the vmstat callback for memory
> > hotplug so maybe split that out and appears unrelated.
>
> not sure I understand. What do you mean?
>
This hunk
@@ -1763,9 +1762,11 @@ static int vmstat_cpu_dead(unsigned int cpu)
static int __init setup_vmstat(void)
{
-#ifdef CONFIG_SMP
- int ret;
+ int ret = 0;
+
+ vmstat_wq = alloc_workqueue("vmstat", WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
+#ifdef CONFIG_SMP
ret = cpuhp_setup_state_nocalls(CPUHP_MM_VMSTAT_DEAD, "mm/vmstat:dead",
NULL, vmstat_cpu_dead);
if (ret < 0)
@@ -1789,7 +1790,7 @@ static int __init setup_vmstat(void)
proc_create("vmstat", S_IRUGO, NULL, &proc_vmstat_file_operations);
proc_create("zoneinfo", S_IRUGO, NULL, &proc_zoneinfo_file_operations);
#endif
- return 0;
+ return ret;
A failed register of vmstat_cpu_dead is returning the failure code in an
init function now. Chances are it'll never hit but it didn't seem related
to the patches general intent.
> > It also feels like vmstat is now a misleading name for something that
> > handles vmstat, lru drains and per-cpu drains but that's cosmetic.
>
> yeah a better name sounds like a good thing. mm_nonblock_wq?
>
it's not always non-blocking. Maybe mm_percpu_wq to describev a workqueue
that handles a variety of MM-related per-cpu updates?
--
Mel Gorman
SUSE Labs
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