linux-kernel - Re: 2.6.22-stable causes oomkiller to be invoked

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Message-ID: <20071230192406.GA10454@linux.vnet.ibm.com>
Date:	Mon, 31 Dec 2007 00:54:06 +0530
From:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Christoph Lameter <clameter@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	htejun@...il.com, gregkh@...e.de,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ibm.com>, maneesh@...ux.vnet.ibm.com,
	lkml <linux-kernel@...r.kernel.org>, stable@...nel.org,
	linux-mm@...ck.org
Subject: Re: 2.6.22-stable causes oomkiller to be invoked

On Sun, Dec 30, 2007 at 03:01:16PM +0100, Ingo Molnar wrote:
> 
> * Christoph Lameter <clameter@....com> wrote:
> 
> > Index: linux-2.6/arch/x86/mm/pgtable_32.c
> > ===================================================================
> > --- linux-2.6.orig/arch/x86/mm/pgtable_32.c	2007-12-26 12:55:10.000000000 -0800
> > +++ linux-2.6/arch/x86/mm/pgtable_32.c	2007-12-26 12:55:54.000000000 -0800
> > @@ -366,6 +366,15 @@ void pgd_free(pgd_t *pgd)
> >  		}
> >  	/* in the non-PAE case, free_pgtables() clears user pgd entries */
> >  	quicklist_free(0, pgd_dtor, pgd);
> > +
> > +	/*
> > +	 * We must call check_pgd_cache() here because the pgd is freed after
> > +	 * tlb flushing and the call to check_pgd_cache. In some cases the VM
> > +	 * may not call tlb_flush_mmu during process termination (??).
> 
> that's incorrect i think: during process termination exit_mmap() calls 
> tlb_finish_mmu() unconditionally which calls tlb_flush_mmu().
> 
> > +	 * If this is repeated then we may never call check_pgd_cache.
> > +	 * The quicklist will grow and grow. So call check_pgd_cache here.
> > +	 */
> > +	check_pgt_cache();
> >  }
> 
> so we still dont seem to understand the failure mode well enough. This 
> also looks like a quite dangerous change so late in the v2.6.24 cycle. 
> Does it really fix the OOM? If yes, why exactly?
> 

No it does not. I've sent out some more information if it helps, will
send to you separately.

-- 
regards,
Dhaval
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