From: Minchan Kim <minchan@kernel.org>
To: John Hubbard <jhubbard@nvidia.com>
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: Fri, 5 Feb 2021 13:28:01 -0800 [thread overview]
Message-ID: <YB24YXMJOjwokDb5@google.com> (raw)
In-Reply-To: <269689b7-3b6d-55dc-9044-fbf2984089ab@nvidia.com>
On Fri, Feb 05, 2021 at 12:25:52PM -0800, John Hubbard wrote:
> On 2/5/21 8:15 AM, Minchan Kim wrote:
> ...
> > > Yes, approximately. I was wondering if this would suffice at least as a baseline:
> > >
> > > cma_alloc_success 125
> > > cma_alloc_failure 25
> >
> > IMO, regardless of the my patch, it would be good to have such statistics
> > in that CMA was born to replace carved out memory with dynamic allocation
> > ideally for memory efficiency ideally so failure should regard critical
> > so admin could notice it how the system is hurt.
>
> Right. So CMA failures are useful for the admin to see, understood.
>
> >
> > Anyway, it's not enough for me and orthgonal with my goal.
> >
>
> OK. But...what *is* your goal, and why is this useless (that's what
> orthogonal really means here) for your goal?
As I mentioned, the goal is to monitor the failure from each of CMA
since they have each own purpose.
Let's have an example.
System has 5 CMA area and each CMA is associated with each
user scenario. They have exclusive CMA area to avoid
fragmentation problem.
CMA-1 depends on bluetooh
CMA-2 depends on WIFI
CMA-3 depends on sensor-A
CMA-4 depends on sensor-B
CMA-5 depends on sensor-C
With this, we could catch which module was affected but with global failure,
I couldn't find who was affected.
>
> Also, would you be willing to try out something simple first,
> such as providing indication that cma is active and it's overall success
> rate, like this:
>
> /proc/vmstat:
>
> cma_alloc_success 125
> cma_alloc_failure 25
>
> ...or is the only way to provide the more detailed items, complete with
> per-CMA details, in a non-debugfs location?
>
>
> > >
> > > ...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)?
> >
> > There is no upper bound since it's configurable.
> >
>
> OK, thanks,so that pretty much rules out putting per-cma details into
> anything other than a directory or something like it.
>
> > >
> > > 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
> >
> > At this moment, allocation/failure for each CMA area since they have
> > particular own usecase, which makes me easy to keep which module will
> > be affected. I think it is very useful per-CMA statistics as minimum
> > code change so I want to enable it by default under CONFIG_CMA && CONFIG_SYSFS.
> >
> > > by a range of allocation sizes is better...
> >
> > I takes your suggestion something like this.
> >
> > [alloc_range] could be order or range by interval
> >
> > /sys/kernel/mm/cma/cma-A/[alloc_range]/success
> > /sys/kernel/mm/cma/cma-A/[alloc_range]/fail
> > ..
> > ..
> > /sys/kernel/mm/cma/cma-Z/[alloc_range]/success
> > /sys/kernel/mm/cma/cma-Z/[alloc_range]/fail
>
> Actually, I meant, "ranges instead of cma areas", like this:
>
> /<path-to-cma-data/[alloc_range_1]/success
> /<path-to-cma-data/[alloc_range_1]/fail
> /<path-to-cma-data/[alloc_range_2]/success
> /<path-to-cma-data/[alloc_range_2]/fail
> ...
> /<path-to-cma-data/[alloc_range_max]/success
> /<path-to-cma-data/[alloc_range_max]/fail
>
> The idea is that knowing the allocation sizes that succeeded
> and failed is maybe even more interesting and useful than
> knowing the cma area that contains them.
Understand your point but it would make hard to find who was
affected by the failure. That's why I suggested to have your
suggestion under additional config since per-cma metric with
simple sucess/failure are enough.
>
> >
> > I agree it would be also useful but I'd like to enable it under
> > CONFIG_CMA_SYSFS_ALLOC_RANGE as separate patchset.
> >
>
> I will stop harassing you very soon, just want to bottom out on
> understanding the real goals first. :)
>
I hope my example makes the goal more clear for you.
next prev parent reply other threads:[~2021-02-05 21:28 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-03 15:50 [PATCH] mm: cma: support sysfs Minchan Kim
2021-02-04 8:50 ` John Hubbard
2021-02-04 20:07 ` Minchan Kim
2021-02-04 23:14 ` John Hubbard
2021-02-04 23:43 ` Suren Baghdasaryan
2021-02-04 23:45 ` Suren Baghdasaryan
2021-02-05 0:25 ` John Hubbard
2021-02-05 0:34 ` John Hubbard
2021-02-05 1:44 ` Suren Baghdasaryan
2021-02-05 0:12 ` Minchan Kim
2021-02-05 0:24 ` John Hubbard
2021-02-05 1:44 ` Minchan Kim
2021-02-05 2:39 ` Suren Baghdasaryan
2021-02-05 2:52 ` John Hubbard
2021-02-05 5:17 ` Minchan Kim
2021-02-05 5:49 ` John Hubbard
2021-02-05 6:24 ` Minchan Kim
2021-02-05 6:41 ` John Hubbard
2021-02-05 16:15 ` Minchan Kim
2021-02-05 20:25 ` John Hubbard
2021-02-05 21:28 ` Minchan Kim [this message]
2021-02-05 21:52 ` Suren Baghdasaryan
2021-02-05 21:58 ` John Hubbard
2021-02-05 22:47 ` Minchan Kim
2021-02-06 17:08 ` Pintu Agarwal
2021-02-08 8:39 ` John Hubbard
2021-02-05 21:57 ` John Hubbard
2021-02-05 2:55 ` Matthew Wilcox
2021-02-05 5:22 ` Minchan Kim
2021-02-05 12:12 ` Matthew Wilcox
2021-02-05 16:16 ` Minchan Kim
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YB24YXMJOjwokDb5@google.com \
--to=minchan@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=gregkh@linuxfoundation.org \
--cc=jhubbard@nvidia.com \
--cc=joaodias@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=surenb@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).