Re: [RFC PATCH 0/3] meminfo: introduce extra meminfo

[Leon Romanovsky <leon@kernel.org>]

On Fri, Mar 13, 2020 at 04:19:36PM +0100, Vlastimil Babka wrote:
> +CC linux-api, please include in future versions as well
>
> On 3/11/20 4:44 AM, Jaewon Kim wrote:
> > /proc/meminfo or show_free_areas does not show full system wide memory
> > usage status. There seems to be huge hidden memory especially on
> > embedded Android system. Because it usually have some HW IP which do not
> > have internal memory and use common DRAM memory.
> >
> > In Android system, most of those hidden memory seems to be vmalloc pages
> > , ion system heap memory, graphics memory, and memory for DRAM based
> > compressed swap storage. They may be shown in other node but it seems to
> > useful if /proc/meminfo shows all those extra memory information. And
> > show_mem also need to print the info in oom situation.
> >
> > Fortunately vmalloc pages is alread shown by commit 97105f0ab7b8
> > ("mm: vmalloc: show number of vmalloc pages in /proc/meminfo"). Swap
> > memory using zsmalloc can be seen through vmstat by commit 91537fee0013
> > ("mm: add NR_ZSMALLOC to vmstat") but not on /proc/meminfo.
> >
> > Memory usage of specific driver can be various so that showing the usage
> > through upstream meminfo.c is not easy. To print the extra memory usage
> > of a driver, introduce following APIs. Each driver needs to count as
> > atomic_long_t.
> >
> > int register_extra_meminfo(atomic_long_t *val, int shift,
> > 			   const char *name);
> > int unregister_extra_meminfo(atomic_long_t *val);
> >
> > Currently register ION system heap allocator and zsmalloc pages.
> > Additionally tested on local graphics driver.
> >
> > i.e) cat /proc/meminfo | tail -3
> > IonSystemHeap:    242620 kB
> > ZsPages:          203860 kB
> > GraphicDriver:    196576 kB
> >
> > i.e.) show_mem on oom
> > <6>[  420.856428]  Mem-Info:
> > <6>[  420.856433]  IonSystemHeap:32813kB ZsPages:44114kB GraphicDriver::13091kB
> > <6>[  420.856450]  active_anon:957205 inactive_anon:159383 isolated_anon:0
>
> I like the idea and the dynamic nature of this, so that drivers not present
> wouldn't add lots of useless zeroes to the output.
> It also makes simpler the decisions of "what is important enough to need its own
> meminfo entry".
>
> The suggestion for hunting per-driver /sys files would only work if there was a
> common name to such files so once can find(1) them easily.
> It also doesn't work for the oom/failed alloc warning output.

Of course there is a need to have a stable name for such an output, this
is why driver/core should be responsible for that and not drivers authors.

The use case which I had in mind slightly different than to look after OOM.

I'm interested to optimize our drivers in their memory footprint to
allow better scale in SR-IOV mode where one device creates many separate
copies of itself. Those copies easily can take gigabytes of RAM due to
the need to optimize for high-performance networking. Sometimes the
amount of memory and not HW is actually limits the scale factor.

So I would imagine this feature being used as an aid for the driver
developers and not for the runtime decisions.

My 2-cents.

Thanks