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

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Message-ID: <20121203190715.GB1377@lenny.home.zabbo.net>
Date:	Mon, 3 Dec 2012 11:07:15 -0800
From:	Zach Brown <zab@...hat.com>
To:	Jeff Moyer <jmoyer@...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

On Mon, Dec 03, 2012 at 11:22:31AM -0500, Jeff Moyer wrote:
> 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?

Heh, indeed.

> 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).  :-)

No argument here,  it just jumped out at me in the code.  I didn't check
out the callers or history of why it was that way :).

- z
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