Re: [PATCH] mm: vmstat: Use zeroed stats for unpopulated zones

[Vlastimil Babka <vbabka@suse.cz>]

On 5/7/20 11:08 AM, Sandipan Das wrote:
>>>
>>> This is certainly an improvement. Thanks! The question whether we can
>>> identify where bogus numbers came from would be interesting as well.
>>> Maybe those are not worth fixing but it would be great to understand
>>> them at least. I have to say that the explanation via boot_pageset is
>>> not really clear to me.
>>>
>> 
>> The documentation update will definitely help. Thanks for that.

Thanks both, will send a proper patch.

>> I did collect some stack traces on a ppc64 guest for calls to zone_statistics()
>> in case of zones that are using the boot_pageset and most of them originate
>> from kmem_cache_init() with eventual calls to allocate_slab().
>> 
>> [    0.000000] [c00000000282b690] [c000000000402d98] zone_statistics+0x138/0x1d0                                                                                                
>> [    0.000000] [c00000000282b740] [c000000000401190] rmqueue_pcplist+0xf0/0x120                                                                                                 
>> [    0.000000] [c00000000282b7d0] [c00000000040b178] get_page_from_freelist+0x2f8/0x2100                                                                                        
>> [    0.000000] [c00000000282bb30] [c000000000401ae0] __alloc_pages_nodemask+0x1a0/0x2d0                                                                                         
>> [    0.000000] [c00000000282bbc0] [c00000000044b040] alloc_slab_page+0x70/0x580                                                                                                 
>> [    0.000000] [c00000000282bc20] [c00000000044b5f8] allocate_slab+0xa8/0x610                                                                                                   
>> ...
>> 
>> In the remaining cases, the sources are ftrace_init() and early_trace_init().
>> 
> 
> Forgot to add that this happens during the period between zone_pcp_init() and setup_zone_pageset().

If you can identify a good moment during the boot when the boot_pageset stops
being used, maybe we could just reset its stats to zero once at that point and
be done with it.

> - Sandipan
>