On 2/4/21 4:25 PM, John Hubbard wrote:
On 2/4/21 3:45 PM, Suren Baghdasaryan wrote:
...
2) The overall CMA allocation attempts/failures (first two items above) seem
an odd pair of things to track. Maybe that is what was easy to track, but I'd
vote for just omitting them.
Then, how to know how often CMA API failed?
Why would you even need to know that, *in addition* to knowing specific
page allocation numbers that failed? Again, there is no real-world motivation
cited yet, just "this is good data". Need more stories and support here.
IMHO it would be very useful to see whether there are multiple
small-order allocation failures or a few large-order ones, especially
for CMA where large allocations are not unusual. For that I believe
both alloc_pages_attempt and alloc_pages_fail would be required.
Sorry, I meant to say "both cma_alloc_fail and alloc_pages_fail would
be required".
So if you want to know that, the existing items are still a little too indirect
to really get it right. You can only know the average allocation size, by
dividing. Instead, we should provide the allocation size, for each count.
The limited interface makes this a little awkward, but using zones/ranges could
work: "for this range of allocation sizes, there were the following stats". Or,
some other technique that I haven't thought of (maybe two items per file?) would
be better.
On the other hand, there's an argument for keeping this minimal and simple. That
would probably lead us to putting in a couple of items into /proc/vmstat, as I
just mentioned in my other response, and calling it good.
...and remember: if we keep it nice and minimal and clean, we can put it into
/proc/vmstat and monitor it.
And then if a problem shows up, the more complex and advanced debugging data can
go into debugfs's CMA area. And you're all set.
If Android made up some policy not to use debugfs, then:
a) that probably won't prevent engineers from using it anyway, for advanced debugging,
and
b) If (a) somehow falls short, then we need to talk about what Android's plans are to
fill the need. And "fill up sysfs with debugfs items, possibly duplicating some of them,
and generally making an unecessary mess, to compensate for not using debugfs" is not
my first choice. :)
thanks,
--
John Hubbard
NVIDIA
