linux-kernel - Re: [patch 4/7] fault-injection capability for alloc

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Date:	Thu, 12 Oct 2006 14:40:42 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, ak@...e.de, Don Mullis <dwm@...r.net>
Subject: Re: [patch 4/7] fault-injection capability for alloc_pages()

On Thu, 12 Oct 2006 16:43:09 +0900
Akinobu Mita <akinobu.mita@...il.com> wrote:

> @@ -1058,6 +1097,9 @@ __alloc_pages(gfp_t gfp_mask, unsigned i
>  
>  	might_sleep_if(wait);
>  
> +	if (should_fail_alloc_page(gfp_mask, order))
> +		return NULL;

In previous work I've done on this I've found that allowing
application-initiated allocations to fail is a right pain: all of userspace
gets all unreliable and applications die all the time.

I realise that it's possible to limit the failures to a particular process,
but it's also possible to let the allocations fail for _all_ processes, in
which case this problem will hurt.

What I found was a reasonable fix for this problem was to limit the
failures to those requests which did not have __GFP_HIGHMEM set.  That way,
userspace allocations work, but kernel-internal allocations are subject to
failures.

That might be worth adding as an additional tunable?
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