Re: [PATCH] mm: cma: support sysfs

From: John Hubbard <jhubbard@nvidia.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	<gregkh@linuxfoundation.org>, <surenb@google.com>,
	<joaodias@google.com>, LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: cma: support sysfs
Date: Thu, 4 Feb 2021 22:41:14 -0800	[thread overview]
Message-ID: <f6e41e39-d60b-764d-0af4-8e6977663821@nvidia.com> (raw)
In-Reply-To: <YBzkjh5nnuNiGb6Q@google.com>

On 2/4/21 10:24 PM, Minchan Kim wrote:
> On Thu, Feb 04, 2021 at 09:49:54PM -0800, John Hubbard wrote:
>> On 2/4/21 9:17 PM, Minchan Kim wrote:
...
>> # cat vmstat | grep -i cma
>> nr_free_cma 261718
>>
>> # cat meminfo | grep -i cma
>> CmaTotal:        1048576 kB
>> CmaFree:         1046872 kB
>>
>> OK, given that CMA is already in those two locations, maybe we should put
>> this information in one or both of those, yes?
> 
> Do you suggest something liks this, for example?
> 
> 
> cat vmstat | grep -i cma
> cma_a_success	125
> cma_a_fail	25
> cma_b_success	130
> cma_b_fail	156
> ..
> cma_f_fail	xxx
> 

Yes, approximately. I was wondering if this would suffice at least as a baseline:

cma_alloc_success   125
cma_alloc_failure   25

...and then, to see if more is needed, some questions:

a)  Do you know of an upper bound on how many cma areas there can be
(I think Matthew also asked that)?

b) Is tracking the cma area really as valuable as other possibilities? We can put
"a few" to "several" items here, so really want to get your very favorite bits of
information in. If, for example, there can be *lots* of cma areas, then maybe tracking
by a range of allocation sizes is better...

thanks,
-- 
John Hubbard
NVIDIA