On 18.02.21 17:47, Minchan Kim wrote:
On Thu, Feb 18, 2021 at 05:26:08PM +0100, David Hildenbrand wrote:
On 18.02.21 17:19, Minchan Kim wrote:
On Thu, Feb 18, 2021 at 10:43:21AM +0100, David Hildenbrand wrote:
On 18.02.21 10:35, Michal Hocko wrote:
On Thu 18-02-21 10:02:43, David Hildenbrand wrote:
On 18.02.21 09:56, Michal Hocko wrote:
On Wed 17-02-21 08:36:03, Minchan Kim wrote:
alloc_contig_range is usually used on cma area or movable zone.
It's critical if the page migration fails on those areas so
dump more debugging message like memory_hotplug unless user
specifiy __GFP_NOWARN.
I agree with David that this has a potential to generate a lot of output
and it is not really clear whether it is worth it. Page isolation code
already has REPORT_FAILURE mode which currently used only for the memory
hotplug because this was just too noisy from the CMA path - d381c54760dc
("mm: only report isolation failures when offlining memory").
Maybe migration failures are less likely to fail but still.
Side note: I really dislike that uncontrolled error reporting on memory
offlining path we have enabled as default. Yeah, it might be useful for
ZONE_MOVABLE in some cases, but otherwise it's just noise.
Just do a "sudo stress-ng --memhotplug 1" and see the log getting flooded
Anyway we can discuss this in a separate thread but I think this is not
a representative workload.
Sure, but the essence is "this is noise", and we'll have more noise on
alloc_contig_range() as we see these calls more frequently. There should be
an explicit way to enable such *debug* messages.
alloc_contig_range already has gfp_mask and it respects __GFP_NOWARN.
I am not 100% sure it does.
Oh, it should. Otherwise, let's fix either of caller or
alloc_contig_range since we have a customer.
```
ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0))
```
Oh, interesting. So I certainly want to add that for virtio-mem as well
- thanks.
And discussed, we should hide the one pr_info... in alloc_contig_range()
as well.
Why shouldn't people use it if they don't care the failure?
Because flooding the log with noise maybe a handful of people on this planet
care about is absolutely useless. With the warnings in warn_alloc() people
can at least conclude something reasonable.
Semantically, it makes sense to me.
About the messeage flooding, shouldn't we go with ratelimiting?
At least that (see warn_alloc()). But I'd even want to see some other
trigger to enable this explicitly on demand.
No objection.
How about adding verbose knob under CONFIG_CMA_DEBUGFS with
alloc_contig_range(..., bool verbose) like start_isolate_page_range?
If admin turns on the verbose mode under CONFIG_CMA_DEBUGFS,
cma_alloc will pass alloc_contig_range(...., true).
I'd handle this internally in alloc_contig_range and not pass magic
flags around. Some kind of debug knob to enable advanced messages
(exceeding the usual allocation warnings we would usually see).
--
Thanks,
David / dhildenb
