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

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Date:   Mon, 18 Mar 2019 14:42:42 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Pankaj Suryawanshi <pankaj.suryawanshi@...fochips.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "minchan@...nel.org" <minchan@...nel.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>
Subject: Re: [External] Re: mm/cma.c: High latency for cma allocation

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On Mon 18-03-19 13:28:50, Pankaj Suryawanshi wrote:
> 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.

Then please collect that data because it is really hard to judge
anything from the numbers you have provided.
-- 
Michal Hocko
SUSE Labs