Re: [PATCH] mm/vmstats: add counters for the page frag cache

[Konstantin Khlebnikov]

On 04.09.2017 04:35, Kyeongdon Kim wrote:
> Thanks for your reply,
> But I couldn't find "NR_FRAGMENT_PAGES" in linux-next.git .. is that vmstat counter? or others?

I mean rather than adding bunch vmstat counters for operations it might be
worth to add page counter which will show current amount of these pages.
But this seems too low-level for tracking, common counters for all network
buffers would be more useful but much harder to implement.

As I can see page owner is able to save stacktrace where allocation happened,
this makes debugging mostly trivial without any counters. If it adds too much
overhead - just track random 1% of pages, should be enough for finding leak.

> As you know, page_frag_alloc() directly calls __alloc_pages_nodemask() function,
> so that makes too difficult to see memory usage in real time even though we have "/meminfo or /slabinfo.." information.
> If there was a way already to figure out the memory leakage from page_frag_cache in mainline, I agree your opinion
> but I think we don't have it now.
>
> If those counters too much in my patch,
> I can say two values (pgfrag_alloc and pgfrag_free) are enough to guess what will happen
> and would remove pgfrag_alloc_calls and pgfrag_free_calls.
>
> Thanks,
> Kyeongdon Kim
>
> On 2017-09-01 ìí 6:12, Konstantin Khlebnikov wrote:
> > IMHO that's too much counters.
> > Per-node NR_FRAGMENT_PAGES should be enough for guessing what's going on.
> > Perf probes provides enough features for furhter debugging.
> >
> > On 01.09.2017 02:37, Kyeongdon Kim wrote:
> > > There was a memory leak problem when we did stressful test
> > > on Android device.
> > > The root cause of this was from page_frag_cache alloc
> > > and it was very hard to find out.
> > >
> > > We add to count the page frag allocation and free with function call.
> > > The gap between pgfrag_alloc and pgfrag_free is good to to calculate
> > > for the amount of page.
> > > The gap between pgfrag_alloc_calls and pgfrag_free_calls is for
> > > sub-indicator.
> > > They can see trends of memory usage during the test.
> > > Without it, it's difficult to check page frag usage so I believe we
> > > should add it.
> > >
> > > Signed-off-by: Kyeongdon Kim <kyeongdon.kim@xxxxxxx>
> > > ---