linux-kernel - Re: [patch -mm 4/9 v2] oom: remove compulsory panic_on

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Date:	Tue, 16 Feb 2010 18:58:17 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Lubos Lunak <l.lunak@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch -mm 4/9 v2] oom: remove compulsory panic_on_oom mode

On Wed, 17 Feb 2010, KAMEZAWA Hiroyuki wrote:

> > We want to lock all populated zones with ZONE_OOM_LOCKED to avoid 
> > needlessly killing more than one task regardless of how many memcgs are 
> > oom.
> > 
> Current implentation archive what memcg want. Why remove and destroy memcg ?
> 

I've updated my patch to not take ZONE_OOM_LOCKED for any zones on memcg 
oom.  I'm hoping that you will add sysctl_panic_on_oom == 2 for this case 
later, however.

> What I mean is
>  - What VM_FAULT_OOM means is not "memory is exhausted" but "something is exhausted".
> 
> For example, when hugepages are all used, it may return VM_FAULT_OOM.
> Especially when nr_overcommit_hugepage == usage_of_hugepage, it returns VM_FAULT_OOM.
> 

The hugetlb case seems to be the only misuse of VM_FAULT_OOM where it 
doesn't mean we simply don't have the memory to handle the page fault, 
i.e. your earlier "memory is exhausted" definition.  That was handled well 
before calling out_of_memory() by simply killing current since we know it 
is faulting hugetlb pages and its resource is limited.

We could pass the vma to pagefault_out_of_memory() and simply kill current 
if its killable and is_vm_hugetlb_page(vma).
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