On Thu, Dec 01, 2016 at 08:38:15AM +0100, Vlastimil Babka wrote:

quoted

quoted

By default config this should not be used on x86.

What do you mean by that statement?

I mean that the 16 mbytes for generic CMA area is not a default on x86:

config CMA_SIZE_MBYTES
         int "Size in Mega Bytes"
         depends on !CMA_SIZE_SEL_PERCENTAGE
         default 0 if X86
         default 16

d7be003a9d275299f5ee36bbdf156654f59e08e9 (v3.18-2122-gd7be003a9d27)
is there the 0MB if-x86 default was added to the tree. Prior to that, it
was 16MiB, and that's where my system picked up the value from.

I have a record of all my kconfigs, because I use oldconfig each time
(going back 8 years to 2.6.27)

# Added in 3.12.0-00001-g5f258d0
CONFIG_CMA=y 
# Added in 3.16.0-rc6-00042-g67dd8f3
CONFIG_CMA_ALIGNMENT=8
CONFIG_CMA_AREAS=7
CONFIG_CMA_SIZE_MBYTES=16
CONFIG_CMA_SIZE_SEL_MBYTES=y
CONFIG_DMA_CMA=y

So the next question, is why did I pick up CMA in
3.16.0-rc6-00042-g67dd8f3... I'll poke at that.

quoted

Yes, I'd say if there's a fallback without much penalty, nowarn makes
sense. If the fallback just tries multiple addresses until success, then
the warning should only be issued when too many attempts have been made.

On the other hand, if the warnings are correlated with high kernel CPU usage, 
it's arguably better to be warned.

Keep the rate-limit on the warning for cases like this?

quoted

quoted

quoted

The rate of the problem starts slow, and also is relatively low on an idle
system (my screens blank at night, no xscreensaver running), but it still ramps
up over time (to the point of generating 2.5GB/hour of "(timestamp)
alloc_contig_range: [83e4d9, 83e4da) PFNs busy"), with various addresses (~100
unique ranges for a day).

My X workload is ~50 chrome tabs and ~20 terminals (over 3x 24" monitors w/ 9
virtual desktops per monitor).

So IIUC, except the messages, everything actually works fine?

There's high kernel CPU usage that seems to roughly correlate with the
messages, but I can't yet tell if that's due to the syslog itself, or
repeated alloc_contig_range requests.

You could try running perf top.

Will do in the morning.

-- 
Robin Hugh Johnson
Gentoo Linux: Dev, Infra Lead, Foundation Trustee & Treasurer
E-Mail   : robbat2@gentoo.org
GnuPG FP : 11ACBA4F 4778E3F6 E4EDF38E B27B944E 34884E85
GnuPG FP : 7D0B3CEB E9B85B1F 825BCECF EE05E6F6 A48F6136

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>