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

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Date:   Tue, 19 Mar 2019 10:29:55 +0000
From:   Pankaj Suryawanshi <pankaj.suryawanshi@...fochips.com>
To:     Michal Hocko <mhocko@...nel.org>
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


________________________________________
From: Michal Hocko <mhocko@...nel.org>
Sent: 18 March 2019 19:59
To: Pankaj Suryawanshi
Cc: linux-mm@...ck.org; linux-kernel@...r.kernel.org; minchan@...nel.org; Kirill Tkhai
Subject: Re: [External] Re: mm/cma.c: High latency for cma allocation

On Mon 18-03-19 14:02:09, Pankaj Suryawanshi wrote:
>> > 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.
>
> Any pointers from which i can get this details ?

I would start by enabling built in tracepoints for the migration or use
a system wide perf monitoring with call graph data.

Calling Sequence is as below.

cma_alloc() -->
alloc_contig_range() -->
start_isolate_page_range() -->
__alloc_contig_migrate_range() -->
isolate_migratepages_range() -->
reclaim_clean_pages_from_list() -->
shrink_page_list()

There is no built in tracepoints except cma_alloc.
How to know where it taking time ?

--
Michal Hocko
SUSE Labs
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