Commit 84861885 authored Jul 12, 2017 by Joel Fernandes Committed by Steven Rostedt (VMware) Jul 19, 2017

tracing/ring_buffer: Try harder to allocate

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

[1] https://marc.info/?l=linux-mm&m=149820805124906&w=2

Link: http://lkml.kernel.org/r/20170713021416.8897-1-joelaf@google.com



Cc: Tim Murray <timmurray@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent 5771a8c0

kernel/trace/ring_buffer.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -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()),
		GFP_KERNEL \| __GFP_NORETRY,
		GFP_KERNEL \| __GFP_RETRY_MAYFAIL,
		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_RETRY_MAYFAIL, 0);
		if (!page)
		goto free_pages;
		bpage->page = page_address(page);