On 07/11/2017 08:05 AM, Joel Fernandes wrote:
> 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
>
> Cc: Alexander Duyck <alexander.h.du...@intel.com>
> Cc: Mel Gorman <mgor...@suse.de>
> Cc: Hao Lee <haolee.sw...@gmail.com>
> Cc: Vladimir Davydov <vdavydov....@gmail.com>
> Cc: Johannes Weiner <han...@cmpxchg.org>
> Cc: Joonsoo Kim <iamjoonsoo....@lge.com>
> Cc: Michal Hocko <mho...@kernel.org>
> Cc: Tim Murray <timmur...@google.com>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: sta...@vger.kernel.org
Not stable, as Michal mentioned.
Acked-by: Vlastimil Babka <vba...@suse.cz>
> Signed-off-by: Joel Fernandes <joe...@google.com>
> ---
> 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()),
> - 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);
>
