Re: [PATCH] mm/zsmalloc: disclose statistics to debugfs

[Ganesh Mahendran <opensource.ganesh@gmail.com>]

2014-12-12 14:40 GMT+08:00 Minchan Kim <minchan@kernel.org>:
> On Fri, Dec 12, 2014 at 01:53:16PM +0800, Ganesh Mahendran wrote:
>> Hello Minchan
>>
>> 2014-12-12 7:40 GMT+08:00 Minchan Kim <minchan@kernel.org>:
>> > Hello Ganesh,
>> >
>> > On Wed, Dec 10, 2014 at 09:40:20PM +0800, Ganesh Mahendran wrote:
>> >> As we now talk more and more about the fragmentation of zsmalloc. But
>> >> we still need to manually add some debug code to see the fragmentation.
>> >> So, I think we may add the statistics of memory fragmention in zsmalloc
>> >> and disclose them to debugfs. Then we can easily get and analysis
>> >> them when adding or developing new feature for zsmalloc.
>> >>
>> >> Below entries will be created when a zsmalloc pool is created:
>> >>     /sys/kernel/debug/zsmalloc/pool-n/obj_allocated
>> >>     /sys/kernel/debug/zsmalloc/pool-n/obj_used
>> >>
>> >> Then the status of objects usage will be:
>> >>     objects_usage = obj_used / obj_allocated
>> >>
>> >
>> > I didn't look at the code in detail but It would be handy for developer
>> > but not sure we should deliver it to admin so need configurable?
>> What kind of configuration do you want?
>> I think it is reasonable to expose such information to admin like
>> */sys/kernel/debug/usb/device*
>>
>> Or maybe we can enclose these code by DEBUG macro which will be
>> defined when CONFIG_ZSMALLOC_DEBUG is selected.
>
> Hmm, I'd like to separte DEBUG and STAT because we can add some
> sanity checking(ex, poisoning for invalid overwriting or
> handle<->obj mapping verification) with DEBUG while we could
> count obj stat with STAT.

Yes. Add a CONFIG_ZSMALLOC_STAT will make code cleaner.

>
> So, now it seems you want CONFIG_ZSMALLOC_STAT?
Yes, I will follow your suggestion.

>
>>
>> >
>> > How about making it per-sizeclass information, not per-pool?
>> Yes, you are right. Per sizeclass information will be better for
>> developers than per pool.
>>
>> Is it acceptable to show 256 lines like:
>> #cat /sys/kernel/debug/zsmalloc/pool-1/obj_in_classes
>> class      obj_allocated     obj_used
>> 1 ...
>> 2 ...
>> ....
>> ....
>> 255
>>
>> Anyway for developers, these information is more usefull.
>
> It would be better to show the number of pages so we can know
> how many of fragment space in last subpage of zspage is wasted.
> But I don't want to keep pages_used in memory but you could
> calcurate it dynamically with obj_allocated when user access debugfs.
>
> #cat /sys/kernel/debug/zsmalloc/pool-1/obj_in_classes
> class-size      obj_allocated     obj_used    pages_used
> 32
> 48
> .
> .
> .

I got it. I will send a v2 patch.

Thanks.
>
> Thanks!
>
> --
> Kind regards,
> Minchan Kim

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