Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH v4] mm: page_alloc: dump migrate-failed pages | Date | Thu, 11 Mar 2021 19:53:01 +0100 |
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On 11.03.21 19:30, Minchan Kim wrote: > Currently, debugging CMA allocation failures is quite limited. > The most commong source of these failures seems to be page
s/commong/common/
> migration which doesn't provide any useful information on the > reason of the failure by itself. alloc_contig_range can report > those failures as it holds a list of migrate-failed pages. > > page refcount, mapcount with page flags on dump_page are > helpful information to deduce the culprit. Furthermore, > dump_page_owner was super helpful to find long term pinner > who initiated the page allocation.
Maybe simply "The information logged by dump_page() has already proven helpful for debugging allocation issues, like identifying long-term pinnings on ZONE_MOVABLE or MIGRATE_CMA."
> > The reason it approach with dynamic debug is the debug message > could emit lots of noises as alloc_contig_range calls more > frequently since it's a best effort allocator.
"Let's use the dynamic debugging infrastructure, such that we avoid flooding the logs and creating a lot of noise on frequent alloc_contig_range() calls. This information is helpful for debugging only."
>>>
> > There are two ifdefery conditions to support common dyndbg options: > > - CONFIG_DYNAMIC_DEBUG_CORE && DYNAMIC_DEBUG_MODULE > It aims for supporting the feature with only specific file > with adding ccflags. > > - CONFIG_DYNAMIC_DEBUG > It aims for supporting the feature with system wide globally. > > A simple example to enable the feature: > > Admin could enable the dump like this(by default, disabled) > > echo "func alloc_contig_dump_pages +p" > control > > Admin could disable it. > > echo "func alloc_contig_dump_pages =_" > control > > Detail goes Documentation/admin-guide/dynamic-debug-howto.rst
<<< I'd drop that completely and only mention:
"For details on dynamic debugging, see Documentation/admin-guide/dynamic-debug-howto.rst."
As you have usage in the code itself, I think you don't have to be repetitive. The ifdeffery seems to be common (e.g., include/linux/netdevice.) for dynamic debugging users, so I don't see the need to describe that in detail.
>>>
> > A concern is utility functions in dump_page uses inconsistent > loglevels. > > __dump_page: KERN_WARNING > __dump_page_owner: KERN_ALERT > stack_trace_print: KERN_DEFAULT > > There are bunch of places to use the inconsistent loglevel > utility functions(e.g., just grep dump_page/strace_trace_print). > It's unfortunate but here we are. It could be addressed > different patchset.
<<< I'd drop that completely and mention
"In the future, we might want to make the loglevels used inside dump_page() consistent and eventually rework the way we log the information here. See [1]"
Where [1] is a link to the discussion.
> > Signed-off-by: Minchan Kim <minchan@kernel.org> > --- > * from v3 - https://lore.kernel.org/linux-mm/20210310180104.517886-1-minchan@kernel.org > * add dyndgb usage comment - akpm > * use dumpstack instead of warn_on - david > > * from v2 - https://lore.kernel.org/linux-mm/20210308202047.1903802-1-minchan@kernel.org/ > * remove ratelimit - mhocko > > * from v1 - https://lore.kernel.org/linux-mm/20210217163603.429062-1-minchan@kernel.org/ > * use dynamic debugging with system wide instead of per-call site - mhocko > > mm/page_alloc.c | 31 +++++++++++++++++++++++++++++++ > 1 file changed, 31 insertions(+) >
Minor nits:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3e4b29ee2b1e..76fc202cb105 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8453,6 +8453,36 @@ static unsigned long pfn_max_align_up(unsigned long pfn) > pageblock_nr_pages)); > } > > +#if defined(CONFIG_DYNAMIC_DEBUG) || \ > + (defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE)) > +/* > + * usage)
"usage)" looks wrong here. Did you mean "Usage:"
> + * dyndbg_dir="/sys/kernel/debug/dynamic_debug" > + * To enable: > + * echo "func alloc_contig_dump_pages +p" > $dyndbg_dir/control > + * To disable: > + * echo "func alloc_contig_dump_pages =_" > $dyndbg_dir/control > + * For detail, read dynamic-debug-howto.rst
Maybe simply
"See admin-guide/dynamic-debug-howto.rst"
> + */ > +static void alloc_contig_dump_pages(struct list_head *page_list) > +{ > + DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, > + "migrate failure");
You can fit that into a single line.
> + > + if (DYNAMIC_DEBUG_BRANCH(descriptor)) { > + struct page *page; > + > + dump_stack(); > + list_for_each_entry(page, page_list, lru) > + dump_page(page, "migration failure"); > + } > +} > +#else > +static inline void alloc_contig_dump_pages(struct list_head *page_list) > +{ > +} > +#endif > + > /* [start, end) must belong to a single zone. */ > static int __alloc_contig_migrate_range(struct compact_control *cc, > unsigned long start, unsigned long end) > @@ -8496,6 +8526,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc, > NULL, (unsigned long)&mtc, cc->mode, MR_CONTIG_RANGE); > } > if (ret < 0) { > + alloc_contig_dump_pages(&cc->migratepages); > putback_movable_pages(&cc->migratepages); > return ret; > } >
As I said, for my taste good enough for now. I would certainly preferred what Michal suggested (e.g., doing it via debug loglevels), but this gets the job done and is not too ugly.
Reviewed-by: David Hildenbrand <david@redhat.com>
-- Thanks,
David / dhildenb
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