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

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Date:   Tue, 11 Jul 2017 13:22:04 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        linux-mm@...ck.org, Alexander Duyck <alexander.h.duyck@...el.com>,
        Mel Gorman <mgorman@...e.de>, Hao Lee <haolee.swjtu@...il.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Michal Hocko <mhocko@...nel.org>,
        Tim Murray <timmurray@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, stable@...r.kernel.org
Subject: Re: [PATCH] tracing/ring_buffer: Try harder to allocate

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@...el.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Hao Lee <haolee.swjtu@...il.com>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Tim Murray <timmurray@...gle.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: stable@...r.kernel.org
> Signed-off-by: Joel Fernandes <joelaf@...gle.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>