ftrace can fail to allocate per-CPU ring buffer on systems with a large number of CPUs coupled while large amounts of cache happening in the page cache. Currently the ring buffer allocation doesn't retry in the VM implementation even if direct-reclaim made some progress but still wasn't able to find a free page. On retrying I see that the allocations almost always succeed. The retry doesn't happen because __GFP_NORETRY is used in the tracer to prevent the case where we might OOM, however if we drop __GFP_NORETRY, we risk destabilizing the system if OOM killer is triggered. To prevent this situation, use the __GFP_DONTOOM flag introduced in earlier patches while droppping __GFP_NORETRY.
With this the following succeed without destabilizing a system with 8 CPU cores and 4GB of memory: echo 100000 > /sys/kernel/debug/tracing/buffer_size_kb On an 8-core system, that would allocate ~800MB. Cc: Alexander Duyck <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Hao Lee <[email protected]> Cc: Vladimir Davydov <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Joonsoo Kim <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: [email protected] Cc: [email protected] Signed-off-by: Joel Fernandes <[email protected]> --- kernel/trace/ring_buffer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 4ae268e687fe..b1cdcac6ca89 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1141,7 +1141,7 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu) * not destabilized. */ bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), - GFP_KERNEL | __GFP_NORETRY, + GFP_KERNEL | __GFP_DONTOOM, cpu_to_node(cpu)); if (!bpage) goto free_pages; @@ -1149,7 +1149,7 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu) list_add(&bpage->list, pages); page = alloc_pages_node(cpu_to_node(cpu), - GFP_KERNEL | __GFP_NORETRY, 0); + GFP_KERNEL | __GFP_DONTOOM, 0); if (!page) goto free_pages; bpage->page = page_address(page); -- 2.13.2.725.g09c95d1e9-goog
