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 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
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 v3 - https://lore.kernel.org/linux-mm/20210310180104.517886-1-minchan@xxxxxxxxxx
* add dyndgb usage comment - akpm
* use dumpstack instead of warn_on - david
* 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 | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
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)
+ * 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
+ */
+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;
+
+ 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;
}
--
2.31.0.rc2.261.g7f71774620-goog
