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

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Message-ID: <3562840.kvm4ZTnunM@vostro.rjw.lan>
Date:	Tue, 27 Nov 2012 22:46:34 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	linux-pm@...r.kernel.org
Cc:	Ming Lei <ming.lei@...onical.com>, 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 Tuesday, November 27, 2012 10:19:29 PM Rafael J. Wysocki wrote:
> On Saturday, November 24, 2012 08:59:14 PM Ming Lei wrote:
> > The patch introduces the flag of memalloc_noio in 'struct dev_pm_info'
> > to help PM core to teach mm not allocating memory with GFP_KERNEL
> > flag for avoiding probable deadlock.
> > 
> > As explained in the comment, any GFP_KERNEL allocation inside
> > runtime_resume() or runtime_suspend() on any one of device in
> > the path from one block or network device to the root device
> > in the device tree may cause deadlock, the introduced
> > pm_runtime_set_memalloc_noio() sets or clears the flag on
> > device in the path recursively.
> > 
> > Cc: Alan Stern <stern@...land.harvard.edu>
> > Cc: "Rafael J. Wysocki" <rjw@...k.pl>
> > Signed-off-by: Ming Lei <ming.lei@...onical.com>
> > ---
> > v5:
> > 	- fix code style error
> > 	- add comment on clear the device memalloc_noio flag
> > v4:
> > 	- rename memalloc_noio_resume as memalloc_noio
> > 	- remove pm_runtime_get_memalloc_noio()
> > 	- add comments on pm_runtime_set_memalloc_noio
> > v3:
> > 	- introduce pm_runtime_get_memalloc_noio()
> > 	- hold one global lock on pm_runtime_set_memalloc_noio
> > 	- hold device power lock when accessing memalloc_noio_resume
> > 	  flag suggested by Alan Stern
> > 	- implement pm_runtime_set_memalloc_noio without recursion
> > 	  suggested by Alan Stern
> > v2:
> > 	- introduce pm_runtime_set_memalloc_noio()
> > ---
> >  drivers/base/power/runtime.c |   60 ++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/pm.h           |    1 +
> >  include/linux/pm_runtime.h   |    3 +++
> >  3 files changed, 64 insertions(+)
> > 
> > diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> > index 3148b10..3e198a0 100644
> > --- a/drivers/base/power/runtime.c
> > +++ b/drivers/base/power/runtime.c
> > @@ -124,6 +124,66 @@ unsigned long pm_runtime_autosuspend_expiration(struct device *dev)
> >  }
> >  EXPORT_SYMBOL_GPL(pm_runtime_autosuspend_expiration);
> >  
> > +static int dev_memalloc_noio(struct device *dev, void *data)
> > +{
> > +	return dev->power.memalloc_noio;
> > +}
> > +
> > +/*
> > + * pm_runtime_set_memalloc_noio - Set a device's memalloc_noio flag.
> > + * @dev: Device to handle.
> > + * @enable: True for setting the flag and False for clearing the flag.
> > + *
> > + * Set the flag for all devices in the path from the device to the
> > + * root device in the device tree if @enable is true, otherwise clear
> > + * the flag for devices in the path whose siblings don't set the flag.
> > + *
> 
> Please use counters instead of walking the whole path every time.  Ie. in
> addition to the flag add a counter to store the number of the device's
> children having that flag set.

I would use the flag only to store the information that
pm_runtime_set_memalloc_noio(dev, true) has been run for this device directly
and I'd use a counter for everything else.

That is, have power.memalloc_count that would be incremented when (1)
pm_runtime_set_memalloc_noio(dev, true) is called for that device and (2) when
power.memalloc_count for one of its children changes from 0 to 1 (and
analogously for decrementation).  Then, check the counter in rpm_callback().

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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