Re: [PATCH] tracing/ring_buffer: Try harder to allocate

[Johannes Weiner]

On Mon, Jul 10, 2017 at 11:05:00PM -0700, 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.duyck@xxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Hao Lee <haolee.swjtu@xxxxxxxxx>
> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Tim Murray <timmurray@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>