netdev - Re: [PATCH v6 2/6] PM / Runtime: introduce pm_runtime_set_memalloc

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Message-ID: <CACVXFVOk45wr8jv3w=KO7uTThGSTSkq0FRsPD6p_AyQZLWGQJg@mail.gmail.com>
Date:	Wed, 28 Nov 2012 17:47:18 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v6 2/6] PM / Runtime: introduce pm_runtime_set_memalloc_noio()

On Wed, Nov 28, 2012 at 5:29 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>
> But it doesn't have to walk the children.  Moreover, with counters it only

Yeah, I got it, it is the advantage of counter, but with extra 'int'
field introduced
in 'struct device'.

> needs to walk the whole path if all devices in it need to be updated.  For
> example, if you call pm_runtime_set_memalloc_noio(dev, true) for a device
> whose parent's counter is greater than zero already, you don't need to
> walk the path above the parent.

We still can do it with the flag only, pm_runtime_set_memalloc_noio(dev, true)
can return immediately if one parent or the 'dev' flag is true.

But considered that the pm_runtime_set_memalloc_noio(dev, false) is only
called in a very infrequent path(network/block device->remove()), looks the
introduced cost isn't worthy of the obtained advantage.

So could you accept not introducing counter? and I will update with the
above improvement you suggested.

Thanks,
--
Ming Lei
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