linux-kernel - Re: [PATCH] kernfs: use stack-buf for small writes.

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Message-ID: <20140923041258.GA27067@mtj.dyndns.org>
Date:	Tue, 23 Sep 2014 00:12:58 -0400
From:	Tejun Heo <tj@...nel.org>
To:	NeilBrown <neilb@...e.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernfs: use stack-buf for small writes.

Hello, Neil.

On Tue, Sep 23, 2014 at 02:06:33PM +1000, NeilBrown wrote:
>  When mdmon needs to update metadata after a device failure in an array
>  there are two 'kmalloc' sources that can trigger deadlock if memory is tight
>  and needs to be written to the array (which cannot be allowed until mdmon
>  updates the metadata).
>  One is in O_DIRECT writes which I have patches for.  The other is when
>  writing to the sysfs file to tell md that it is safe to continue.
>  This simple patch removes the second.

Ugh... :( If this can't be avoided at all, I'd much prefer it to be
something explicit - a flag marking the file as needing a persistent
write buffer which is allocated on open.  "Small" writes on stack
feels way to implicit to me.

Thanks.

-- 
tejun
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