linux-kernel - Re: [PATCH v8] mm: Add memory allocation watchdog kernel thread.

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Message-Id: <201704062002.FAE18212.OJOFOHLStFVFQM@I-love.SAKURA.ne.jp>
Date:   Thu, 6 Apr 2017 20:02:24 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        mhocko@...nel.org, hannes@...xchg.org, mgorman@...hsingularity.net,
        david@...morbit.com, apolyakov@...et.ru, lists@...singer.com,
        hughd@...gle.com
Subject: Re: [PATCH v8] mm: Add memory allocation watchdog kernel thread.

Andrew, anything else I can do?

Tetsuo Handa wrote:
>   Regarding maintenance burden, I consider this patch is least invasive
>   because it does not make __GFP_NOWARN flag's semantic confusing while
>   providing administrators some hints [4]. Also, this patch will remain
>   useful because we might overlook something that can cause infinite
>   loop (or significant delay) in future changes, and we can remove this
>   patch when we achieve safe and robust memory management subsystem.
> 
> Changes from v7 [11]:
> 
>   (1) Reflect review comments from Andrew Morton. (Convert "u8 type" to
>       "bool report", use CPUHP_PAGE_ALLOC_DEAD event and replace
>       for_each_possible_cpu() with for_each_online_cpu(), reuse existing
>       rcu_lock_break() and hung_timeout_jiffies() for now, update comments).

We are still sometimes overlooking unexpected delays like
http://lkml.kernel.org/r/alpine.LSU.2.11.1704051331420.4288@eggly.anvils and
http://lkml.kernel.org/r/da13c3c7-b514-67b0-2eb9-6d6af277901b@wiesinger.com
and I think we will in the future. I believe that this patch is helpful for
catching such cases.