Re: [PATCH] fix spurious OOM kills

From: Andrea Arcangeli <andrea@novell.com>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Nick Piggin <piggin@cyberone.com.au>,
	Rik van Riel <riel@redhat.com>,
	Martin MOKREJ? <mmokrejs@ribosome.natur.cuni.cz>,
	tglx@linutronix.de
Subject: Re: [PATCH] fix spurious OOM kills
Date: Thu, 11 Nov 2004 16:42:38 +0100	[thread overview]
Message-ID: <20041111154238.GD18365@x30.random> (raw)
In-Reply-To: <20041111112922.GA15948@logos.cnet>

On Thu, Nov 11, 2004 at 09:29:22AM -0200, Marcelo Tosatti wrote:
> Hi,
> 
> This is an improved version of OOM-kill-from-kswapd patch.
> 
> I believe triggering the OOM killer from task reclaim context 
> is broken because the chances that it happens increases as the amount
> of tasks inside reclaim increases - and that approach ignores efforts 
> being done by kswapd, who is the main entity responsible for
> freeing pages.
> 
> There have been a few problems pointed out by others (Andrea, Nick) on the 
> last patch - this one solves them.

I disagree about the design of killing anything from kswapd. kswapd is
an async helper like pdflush and it has no knowledge on the caller (it
cannot know if the caller is ok with the memory currently available in
the freelists, before triggering the oom). I'm just about to move the
oom killing away from vmscan.c to page_alloc.c which is basically the
opposite of moving the oom invocation from the task context to kswapd.
page_alloc.c in the task context is the only one who can know if
something has to be killed, vmscan.c cannot know. vmscan.c can only know
if something is still freeable, but if something isn't freeable it
doesn't mean that we've to kill anything (for example if a task exited
or some dma or normal-zone or highmem memory was released by another
task while we were paging waiting for I/O). Every allocation is
different and page_alloc.c is the only one who knows what has to be done
for every single allocation.