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From: Joel Fernandes <>
	Joel Fernandes <>,
	Tim Murray <>, Ingo Molnar <>,
	Steven Rostedt <>,
	Andrew Morton <>
Subject: [for-next][PATCH v2] tracing/ring_buffer: Try harder to allocate
Date: Wed, 12 Jul 2017 19:14:16 -0700	[thread overview]
Message-ID: <> (raw)

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_RETRY_MAYFAIL flag
introduced recently [1].

Tested the following still succeeds without destabilizing a system with
1GB memory.
echo 300000 > /sys/kernel/debug/tracing/buffer_size_kb


Cc: Tim Murray <>
Cc: Ingo Molnar <>
Cc: Steven Rostedt <>
Cc: Andrew Morton <>
Acked-by: Vlastimil Babka <>
Acked-by: Johannes Weiner <>
Acked-by: Michal Hocko <>
Signed-off-by: Joel Fernandes <>
changes since v1:
Added acks and dropped stable

 kernel/trace/ring_buffer.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 4ae268e687fe..529cc50d7243 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1136,12 +1136,12 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
 	for (i = 0; i < nr_pages; i++) {
 		struct page *page;
-		 * __GFP_NORETRY flag makes sure that the allocation fails
-		 * gracefully without invoking oom-killer and the system is
-		 * not destabilized.
+		 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
+		 * gracefully without invoking oom-killer and the system is not
+		 * destabilized.
 		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
 		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),
 		if (!page)
 			goto free_pages;
 		bpage->page = page_address(page);

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                 reply	other threads:[~2017-07-13  2:14 UTC|newest]

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