Re: [External] Re: mm/cma.c: High latency for cma allocation

[Pankaj Suryawanshi <pankaj.suryawanshi@xxxxxxxxxxxxxx>]

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From: Michal Hocko <mhocko@xxxxxxxxxx>
Sent: 18 March 2019 18:37:57
To: Pankaj Suryawanshi
Cc: linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; minchan@xxxxxxxxxx; Kirill Tkhai
Subject: [External] Re: mm/cma.c: High latency for cma allocation

 

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On Mon 18-03-19 12:58:28, Pankaj Suryawanshi wrote:
> Hello,
>
> I am facing issue of high latency in CMA allocation of large size buffer.
>
> I am frequently allocating/deallocation CMA memory, latency of allocation is very high.
>
> Below are the stat for allocation/deallocation latency issue.
>
> (390100 kB),  latency 29997 us
> (390100 kB),  latency 22957 us
> (390100 kB),  latency 25735 us
> (390100 kB),  latency 12736 us
> (390100 kB),  latency 26009 us
> (390100 kB),  latency 18058 us
> (390100 kB),  latency 27997 us
> (16 kB), latency 560 us
> (256 kB), latency 280 us
> (4 kB), latency 311 us
>
> I am using kernel 4.14.65 with android pie(9.0).
>
> Is there any workaround or solution for this(cma_alloc latency) issue ?

Do you have any more detailed information on where the time is spent?
E.g. migration tracepoints?

Hello Michal,

I have the system(vanilla kernel) with 2GB of RAM, reserved 1GB for CMA. No swap or zram.

Sorry, I don't have information where the time is spent.

time is calculated in between cma_alloc call.

I have just cma_alloc trace information/function graph.

 
--
Michal Hocko
SUSE Labs

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