Before the change page_owner recursion was detected via fetching
backtrace and inspecting it for current instruction pointer.
It has a few problems:
- it is slightly slow as it requires extra backtrace and a linear
stack scan of the result
- it is too late to check if backtrace fetching required memory
allocation itself (ia64's unwinder requires it).
To simplify recursion tracking let's use page_owner recursion flag
in 'struct task_struct'.
The change make page_owner=on work on ia64 by avoiding infinite
recursion in:
kmalloc()
-> __set_page_owner()
-> save_stack()
-> unwind() [ia64-specific]
-> build_script()
-> kmalloc()
-> __set_page_owner() [we short-circuit here]
-> save_stack()
-> unwind() [recursion]
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Juri Lelli <juri.lelli@xxxxxxxxxx>
CC: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
CC: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ben Segall <bsegall@xxxxxxxxxx>
CC: Mel Gorman <mgorman@xxxxxxx>
CC: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: linux-mm@xxxxxxxxx
Signed-off-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>
---
Change since v1:
- use bit from task_struct instead of a new field
- track only one recursion depth level so far
include/linux/sched.h | 4 ++++
mm/page_owner.c | 32 ++++++++++----------------------
2 files changed, 14 insertions(+), 22 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ef00bb22164c..00986450677c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -841,6 +841,10 @@ struct task_struct {
/* Stalled due to lack of memory */
unsigned in_memstall:1;
#endif
+#ifdef CONFIG_PAGE_OWNER
+ /* Used by page_owner=on to detect recursion in page tracking. */
+ unsigned in_page_owner:1;
+#endif
unsigned long atomic_flags; /* Flags requiring atomic access. */
diff --git a/mm/page_owner.c b/mm/page_owner.c
index 7147fd34a948..64b2e4c6afb7 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -97,42 +97,30 @@ static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
return (void *)page_ext + page_owner_ops.offset;
}
-static inline bool check_recursive_alloc(unsigned long *entries,
- unsigned int nr_entries,
- unsigned long ip)
-{
- unsigned int i;
-
- for (i = 0; i < nr_entries; i++) {
- if (entries[i] == ip)
- return true;
- }
- return false;
-}
-
static noinline depot_stack_handle_t save_stack(gfp_t flags)
{
unsigned long entries[PAGE_OWNER_STACK_DEPTH];
depot_stack_handle_t handle;
unsigned int nr_entries;
- nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
-
/*
- * We need to check recursion here because our request to
- * stackdepot could trigger memory allocation to save new
- * entry. New memory allocation would reach here and call
- * stack_depot_save_entries() again if we don't catch it. There is
- * still not enough memory in stackdepot so it would try to
- * allocate memory again and loop forever.
+ * Avoid recursion.
+ *
+ * Sometimes page metadata allocation tracking requires more
+ * memory to be allocated:
+ * - when new stack trace is saved to stack depot
+ * - when backtrace itself is calculated (ia64)
*/
- if (check_recursive_alloc(entries, nr_entries, _RET_IP_))
+ if (current->in_page_owner)
return dummy_handle;
+ current->in_page_owner = 1;
+ nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
handle = stack_depot_save(entries, nr_entries, flags);
if (!handle)
handle = failure_handle;
+ current->in_page_owner = 0;
return handle;
}
--
2.31.1
