On Thu, Mar 11, 2021 at 05:40:35PM +0100, David Hildenbrand wrote: > 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@xxxxxxxxxx> > > --- > > * from v2 - https://lore.kernel.org/linux-mm/20210308202047.1903802-1-minchan@xxxxxxxxxx/ > > * remove ratelimit - mhocko > > > > * from v1 - https://lore.kernel.org/linux-mm/20210217163603.429062-1-minchan@xxxxxxxxxx/ > > * 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. Good point. > > Some other way to dump the current call stack would be handy ... Yub, let's go with 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 +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. Let me send next revision with addressing your point and Andrew's one.
