Messages in this thread | | | Subject | Re: [PATCH v3] mm: page_alloc: dump migrate-failed pages | From | David Hildenbrand <> | Date | Thu, 11 Mar 2021 17:40:35 +0100 |
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On 10.03.21 19:01, Minchan Kim wrote: > Currently, debugging CMA allocation failures is quite limited. > The most commong source of these failures seems to be page > 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. > > 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. > > 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 dump_migrate_failure_pages +p" > control > > Admin could disable it. > > echo "func dump_migrate_failure_pages =_" > control > > Detail goes Documentation/admin-guide/dynamic-debug-howto.rst > > 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. > > Signed-off-by: Minchan Kim <minchan@kernel.org> > --- > * 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 | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 3e4b29ee2b1e..f42f3e208794 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8453,6 +8453,27 @@ 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)) > +static void alloc_contig_dump_pages(struct list_head *page_list) > +{ > + DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, > + "migrate failure"); > + > + if (DYNAMIC_DEBUG_BRANCH(descriptor)) { > + struct page *page; > + > + WARN(1, "failed callstack");
Not sure if we want that here. You can deterministically crash a kernel with panic_on_warn set - which is what some distros already do.
Some other way to dump the current call stack would be handy ...
> + 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 +8517,7 @@ 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; > } >
For me, this is good enough for now.
-- Thanks,
David / dhildenb
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