linux-kernel - Re: [patch] bdi: add a user-tunable cpu

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Message-ID: <x49vccjnm0o.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 03 Dec 2012 11:22:31 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Zach Brown <zab@...hat.com>
Cc:	Jens Axboe <jaxboe@...ionio.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch] bdi: add a user-tunable cpu_list for the bdi flusher threads

Jeff Moyer <jmoyer@...hat.com> writes:

>>> +		bdi->flusher_cpumask = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
>>> +		if (!bdi->flusher_cpumask)
>>> +			return -ENOMEM;
>>
>> The bare GFP_KERNEL raises an eyebrow.  Some bdi_init() callers like
>> blk_alloc_queue_node() look like they'll want to pass in a gfp_t for the
>> allocation.
>
> I'd be surprised if that was necessary, seeing how every single caller
> of blk_alloc_queue_node passes in GFP_KERNEL.  I'll make the change,
> though, there aren't too many callers of bdi_init out there.

No other callers of bdi_init want anything but GFP_KERNEL.  In the case
of blk_alloc_queue_node, even *it* doesn't honor the gfp_t passed in!
Have a look at blkcg_init_queue (called from blk_alloc_queue_node) to
see what I mean.  Maybe that's a bug?

I've written the patch to modify bdi_init to take a gfp_t, but I'm
actually not in favor of this change, so I'm not going to post it
(unless, of course, you can provide a compelling argument).  :-)

Cheers,
Jeff
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