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 <[email protected]> CC: Peter Zijlstra <[email protected]> CC: Juri Lelli <[email protected]> CC: Vincent Guittot <[email protected]> CC: Dietmar Eggemann <[email protected]> CC: Steven Rostedt <[email protected]> CC: Ben Segall <[email protected]> CC: Mel Gorman <[email protected]> CC: Daniel Bristot de Oliveira <[email protected]> CC: Andrew Morton <[email protected]> CC: [email protected] Signed-off-by: Sergei Trofimovich <[email protected]> --- 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
