linux-kernel - Re: [PATCH 2/4] oom: Do not invoke oom notifiers on sysrq+f

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Date:	Wed, 8 Jul 2015 16:37:49 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...e.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jakob Unterwurzacher <jakobunt@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 2/4] oom: Do not invoke oom notifiers on sysrq+f

On Wed, 8 Jul 2015, Michal Hocko wrote:

> From: Michal Hocko <mhocko@...e.cz>
> 
> A github user rfjakob has reported the following issue via IRC.
> <rfjakob> Manually triggering the OOM killer does not work anymore in 4.0.5
> <rfjakob> This is what it looks like: https://gist.github.com/rfjakob/346b7dc611fc3cdf4011
> <rfjakob> Basically, what happens is that the GPU driver frees some memory, that satisfies the OOM killer
> <rfjakob> But the memory is allocated immediately again, and in the, no processes are killed no matter how often you trigger the oom killer
> <rfjakob> "in the end"
> 
> Quoting from the github:
> "
> [19291.202062] sysrq: SysRq : Manual OOM execution
> [19291.208335] Purging GPU memory, 74399744 bytes freed, 8728576 bytes still pinned.
> [19291.390767] sysrq: SysRq : Manual OOM execution
> [19291.396792] Purging GPU memory, 74452992 bytes freed, 8728576 bytes still pinned.
> [19291.560349] sysrq: SysRq : Manual OOM execution
> [19291.566018] Purging GPU memory, 75489280 bytes freed, 8728576 bytes still pinned.
> [19291.729944] sysrq: SysRq : Manual OOM execution
> [19291.735686] Purging GPU memory, 74399744 bytes freed, 8728576 bytes still pinned.
> [19291.918637] sysrq: SysRq : Manual OOM execution
> [19291.924299] Purging GPU memory, 74403840 bytes freed, 8728576 bytes still pinned.
> "
> 
> The issue is that sysrq+f (force_kill) gets confused by the regular OOM
> heuristic which tries to prevent from OOM killer if some of the oom
> notifier can relase a memory. The heuristic doesn't make much sense for
> the sysrq+f path because this one is used by the administrator to kill
> a memory hog.
> 
> Reported-by: Jakob Unterwurzacher <jakobunt@...il.com>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Nack, the oom notify list has no place in the oom killer, it should be 
called in the page allocator before calling out_of_memory().  
out_of_memory() should serve a single, well defined purpose: kill a 
process.  If this were done, you wouldn't need random hacks like this in 
place.  This also shouldn't be included in a patchset that redefines the 
semantics of a forced oom kill, which is quite separate.
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