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

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Message-ID: <20071230140116.GC21106@elte.hu>
Date:	Sun, 30 Dec 2007 15:01:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <clameter@....com>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.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


* 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?

	Ingo
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