[CC Vlastimil, Joonsoo]
On Thu 29-06-17 17:47:05, Robin H. Johnson wrote:
> CC'd back to LKML.
>
> On Thu, Jun 29, 2017 at 06:11:00PM +0530, Kumar Abhishek wrote:
> > Hi Robin,
> >
> > I am an independent developer who stumbled upon your thread on the LKML
> > after facing a similar issue - my kernel log being spammed by
> > alloc_contig_range messages. I am running Linux on an ARM system
> > (specifically the BeagleBoard-X15) and am on kernel version 4.9.33 with TI
> > patches on top of it.
> >
> > I am running Debian Stretch (9.0) on the system.
> >
> > Here's what my stack trace looks like:
> ..
> >
> > It's somewhat similar to your stack trace, but this here happens on an
> > etnaviv GPU (Vivante GCxx).
> >
> > In my case if I do 'sudo service lightdm stop', these messages stop too.
> > This seems to suggest that the problem may be in the X server rather than
> > the kernel? I seem to think this because I replicated this on an entirely
> > different set of hardware than yours.
> >
> > I just wanted to bring this to your notice, and also ask you if you managed
> > to solve it for yourself.
> >
> > One solution could be to demote the pr_info in alloc_contig_range to
> > pr_debug or to do away with the message altogether, but this would be
> > suppressing the issue instead of really knowing what it is about.
> >
> > Let me know how I could further investigate this.
> The problem, as far as I got diagnosed on LKML, is that some of the GPUs
> have a bunch of non-fatal contiguous memory allocation requests: they
> have a meaningful fallback path on the allocation, so 'PFNs busy' is a
> false busy for their case.
Well, later on we found out that a change to the compaction has changed
a picture and 424f6c4818bb ("mm: alloc_contig: re-allow CMA to compact
FS pages") fixed that issue. It went to 4.10 and I do not see it in 4.9
stable tree. Maybe it can help in this case as well.
> However, if there was a another consumer that does NOT have a fallback,
> the output would still be crucially useful.
>
> Attached is the patch that I unsuccessfully proposed on LKML to
> rate-limit the messages, with the last revision to only dump_stack() if
> CONFIG_CMA_DEBUG was set.
The patch makes some sense to me in general. Try to repost it.
> The path that LKML wanted was to add a new parameter to suppress or at
> least demote the failure message, and update all of the callers: but it
> means that many of the indirect callers need that added parameter as
> well.
>
> mm/cma.c:cma_alloc this call can suppress the error, you can see it retry.
> mm/hugetlb.c: These callers should get the error message.
>
> The error message DOES still have a good general use in notifying you
> that something is going wrong. There was noticeable performance slowdown
> in my case when it was trying hard to allocate.
>
> --
> Robin Hugh Johnson
> E-Mail : robbat2@xxxxxxxxxxxxxxxxxx
> Home Page : http://www.orbis-terrarum.net/?l=people.robbat2
> ICQ# : 30269588 or 41961639
> GnuPG FP : 11ACBA4F 4778E3F6 E4EDF38E B27B944E 34884E85
> commit 808c209dc82ce79147122ca78e7047bc74a16149
> Author: Robin H. Johnson <robbat2@xxxxxxxxxx>
> Date: Wed Nov 30 10:32:57 2016 -0800
>
> mm: ratelimit & trace PFNs busy.
>
> Signed-off-by: Robin H. Johnson <robbat2@xxxxxxxxxx>
> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6de9440e3ae2..3c28ec3d18f8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7289,8 +7289,16 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>
> /* Make sure the range is really isolated. */
> if (test_pages_isolated(outer_start, end, false)) {
> - pr_info("%s: [%lx, %lx) PFNs busy\n",
> - __func__, outer_start, end);
> + static DEFINE_RATELIMIT_STATE(ratelimit_pfn_busy,
> + DEFAULT_RATELIMIT_INTERVAL,
> + DEFAULT_RATELIMIT_BURST);
> + if (__ratelimit(&ratelimit_pfn_busy)) {
> + pr_info("%s: [%lx, %lx) PFNs busy\n",
> + __func__, outer_start, end);
> + if (IS_ENABLED(CONFIG_CMA_DEBUG))
> + dump_stack();
> + }
> +
> ret = -EBUSY;
> goto done;
> }
--
Michal Hocko
SUSE Labs
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