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

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Date:   Fri, 13 Mar 2020 09:21:22 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jaewon Kim <jaewon31.kim@...sung.com>
Cc:     adobriyan@...il.com, akpm@...ux-foundation.org, labbott@...hat.com,
        sumit.semwal@...aro.org, minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jaewon31.kim@...il.com
Subject: Re: [RFC PATCH 0/3] meminfo: introduce extra meminfo

On Fri, Mar 13, 2020 at 01:39:14PM +0900, Jaewon Kim wrote:
>
>
> On 2020년 03월 11일 16:25, Leon Romanovsky wrote:
> > On Wed, Mar 11, 2020 at 12:44:38PM +0900, 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
> > The idea is nice and helpful, but I'm sure that the interface will be abused
> > almost immediately. I expect that every driver will register to such API.
> >
> > First it will be done by "large" drivers and after that everyone will copy/paste.
> I thought using it is up to driver developers.
> If it is abused, /proc/meminfo will show too much info. for that device.
> What about a new node, /proc/meminfo_extra, to gather those info. and not
> corrupting original /proc/meminfo.

I don't know if it is applicable for all users, but for the drivers
such info is better to be placed in /sys/ as separate file (for example
/sys/class/net/wlp3s0/*) and driver/core will be responsible to
register/unregister.

It will ensure that all drivers get this info without need to register
and make /proc/meminfo and /proc/meminfo_extra too large.

Thanks

>
> Thank you
> > Thanks
> >
> >
>