linux-kernel - Re: [patch 1/6] md: remove dependency on __GFP

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Message-Id: <20100823122606.47524cef.akpm@linux-foundation.org>
Date:	Mon, 23 Aug 2010 12:26:06 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Neil Brown <neilb@...e.de>, Alasdair G Kergon <agk@...hat.com>,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/6] md: remove dependency on __GFP_NOFAIL

On Mon, 16 Aug 2010 19:57:51 -0700 (PDT)
David Rientjes <rientjes@...gle.com> wrote:

> Removes the dependency on __GFP_NOFAIL by looping indefinitely in the
> caller.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  drivers/md/dm-region-hash.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-region-hash.c b/drivers/md/dm-region-hash.c
> --- a/drivers/md/dm-region-hash.c
> +++ b/drivers/md/dm-region-hash.c
> @@ -289,8 +289,12 @@ static struct dm_region *__rh_alloc(struct dm_region_hash *rh, region_t region)
>  	struct dm_region *reg, *nreg;
>  
>  	nreg = mempool_alloc(rh->region_pool, GFP_ATOMIC);
> -	if (unlikely(!nreg))
> -		nreg = kmalloc(sizeof(*nreg), GFP_NOIO | __GFP_NOFAIL);
> +	if (unlikely(!nreg)) {
> +		/* FIXME: this may potentially loop forever */
> +		do {
> +			nreg = kmalloc(sizeof(*nreg), GFP_NOIO);
> +		} while (!nreg);
> +	}
>  
>  	nreg->state = rh->log->type->in_sync(rh->log, region, 1) ?
>  		      DM_RH_CLEAN : DM_RH_NOSYNC;

erm.

The reason for adding GFP_NOFAIL in the first place was my observation
that the kernel contained lots of open-coded retry-for-ever loops.

All of these are wrong, bad, buggy and mustfix.  So we consolidated the
wrongbadbuggymustfix concept into the core MM so that miscreants could
be easily identified and hopefully fixed.

I think that simply undoing that change is a bad idea - it allows the
wrongbadbuggymustfix code to hide from view.

The correct way to remove __GFP_NOFAIL is to fix the
wrongbadbuggymustfix code properly.
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