linux-kernel - Re: [PATCH v7 0/6] solve deadlock caused by memory allocation with I/O

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Date:	Thu, 17 Jan 2013 13:57:26 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-mm@...ck.org, Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Jens Axboe <axboe@...nel.dk>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v7 0/6] solve deadlock caused by memory allocation with
 I/O

On Thu, 17 Jan 2013 09:28:14 +0800
Ming Lei <ming.lei@...onical.com> wrote:

> > If so, I wonder if we could avoid the whole problem by appropriately
> > syncing all dirty memory back to storage before starting to turn devices
> > off?
> 
> The patchset is to address the probable deadlock problem by GFP_KERNEL
> during runtime suspend/resume which is per block/network device. I am
> wondering if syncing all dirty memory is suitable or necessary during
> per-storage/network device runtime resume/suspend:
> 
>       - sys_sync is very slow and runtime pm operation is frequent
> 
>       - it is not efficient because only sync dirty memory against the affected
>         device is needed in theory and not necessary to sync all
> 
>      - we still need some synchronization to avoid accessing the storage
>        between sys_sync and device suspend, just like system sleep case,
>        pm_restrict_gfp_mask is needed even sys_sync has been done
>        inside enter_state().
> 
> So looks the approach in the patch is simpler and more efficient, :-)
> 
> Also, with the patchset, we can avoid many GFP_NOIO allocation
> which is fragile and not easy to use.

Fair enough, thanks.

I grabbed the patches for 3.9-rc1.  It is good that the page
allocator's newly-added test of current->flags is not on the fastpath.

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