Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210203155001.4121868-1-minchan@kernel.org> <7e7c01a7-27fe-00a3-f67f-8bcf9ef3eae9@nvidia.com>
 <YBxT9XFE6QAQ4T9N@google.com> <cda5547b-0c78-756b-bd0c-f3e534d04bff@nvidia.com>
 <YByNU4Q7cc7gYwPh@google.com> <87d7ec1f-d892-0491-a2de-3d0feecca647@nvidia.com>
 <YByi/gdaGJeV/+8b@google.com>
In-Reply-To: <YByi/gdaGJeV/+8b@google.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 4 Feb 2021 18:39:47 -0800
Message-ID: <CAJuCfpHmMVFDZ7ZA0uVc_5b4HCB3QBptahBhTWovGvNtjmfGig@mail.gmail.com>
Subject: Re: [PATCH] mm: cma: support sysfs
To:     Minchan Kim <minchan@kernel.org>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        John Dias <joaodias@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Feb 4, 2021 at 5:44 PM Minchan Kim <minchan@kernel.org> wrote:
>
> On Thu, Feb 04, 2021 at 04:24:20PM -0800, John Hubbard wrote:
> > On 2/4/21 4:12 PM, Minchan Kim wrote:
> > ...
> > > > > Then, how to know how often CMA API failed?
> > > >
> > > > Why would you even need to know that, *in addition* to knowing specific
> > > > page allocation numbers that failed? Again, there is no real-world motivation
> > > > cited yet, just "this is good data". Need more stories and support here.
> > >
> > > Let me give an example.
> > >
> > > Let' assume we use memory buffer allocation via CMA for bluetooth
> > > enable of  device.
> > > If user clicks the bluetooth button in the phone but fail to allocate
> > > the memory from CMA, user will still see bluetooth button gray.
> > > User would think his touch was not enough powerful so he try clicking
> > > again and fortunately CMA allocation was successful this time and
> > > they will see bluetooh button enabled and could listen the music.
> > >
> > > Here, product team needs to monitor how often CMA alloc failed so
> > > if the failure ratio is steadily increased than the bar,
> > > it means engineers need to go investigation.
> > >
> > > Make sense?
> > >
> >
> > Yes, except that it raises more questions:
> >
> > 1) Isn't this just standard allocation failure? Don't you already have a way
> > to track that?
> >
> > Presumably, having the source code, you can easily deduce that a bluetooth
> > allocation failure goes directly to a CMA allocation failure, right?
> >
> > Anyway, even though the above is still a little murky, I expect you're right
> > that it's good to have *some* indication, somewhere about CMA behavior...
> >
> > Thinking about this some more, I wonder if this is really /proc/vmstat sort
> > of data that we're talking about. It seems to fit right in there, yes?
>
> Thing is CMA instance are multiple, cma-A, cma-B, cma-C and each of CMA
> heap has own specific scenario. /proc/vmstat could be bloated a lot
> while CMA instance will be increased.

Oh, I missed the fact that you need these stats per-CMA.