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Date:   Fri, 20 Mar 2020 18:00:26 +0800
From:   Dave Young <dyoung@redhat.com>
To:     Jaewon Kim <jaewon31.kim@samsung.com>
Cc:     adobriyan@gmail.com, akpm@linux-foundation.org, labbott@redhat.com,
        sumit.semwal@linaro.org, minchan@kernel.org, ngupta@vflare.org,
        sergey.senozhatsky.work@gmail.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com,
        kexec@lists.infradead.org, kasong@redhat.com, bhe@redhat.com
Subject: Re: [RFC PATCH 0/3] meminfo: introduce extra meminfo
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On 03/11/20 at 12:44pm, 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

Kdump is also a use case for having a better memory use info, it runs
with limited memory, and we see more oom cases from device drivers
instead of userspace processes.

I think this might be helpful if drivers can implement and register the
hook.  But it would be ideal if we can have some tracing code to trace
the memory alloc/free and get the memory use info automatically.

Anyway the proposal is better than none, thumb up!

Let me cc Kairui who is working on kdump oom issues.

Thanks
Dave