Date: Wed, 2 Dec 2009 22:11:07 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>,
       pm list <linux-pm@lists.linux-foundation.org>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       Kernel Testers List <kernel-testers@vger.kernel.org>,
       Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH] uswsusp: automatically free the in-memory image once
 s2disk has finished with it
Message-ID: <20091202211107.GA20830@elf.ucw.cz>
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On Wed 2009-12-02 14:28:12, Alan Jenkins wrote:
> The original in-kernel suspend (swsusp) frees the in-memory hibernation
> image before powering off the machine.  s2disk doesn't, so there is
> _much_ less free memory when it tries to power off.
> 
> This is a gratuitous difference.  The userspace suspend interface
> /dev/snapshot only allows the hibernation image to be read once.
> Once the s2disk program has read the last page, we can free the entire
> image.
> 
> This avoids a hang after writing the hibernation image which was
> triggered by commit 5f8dcc21211a3d4e3a7a5ca366b469fb88117f61
> "page-allocator: split per-cpu list into one-list-per-migrate-type":

Yes, you work around page-allocator hang. But is it right thing to do?

I mean... Power down should not be too memory-critical. Why can't new
page allocator handle that?

(And yes, when page allocator is fixed we may want to do something
like that, but...)

								Pavel

> --- a/kernel/power/user.c
> +++ b/kernel/power/user.c
> @@ -165,6 +165,10 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
> 			res = -EFAULT;
> 		else
> 			*offp = data->handle.offset;
> +	} else {
> +		swsusp_free();
> +		memset(&data->handle, 0, sizeof(struct snapshot_handle));
> +		data->ready = 0;
> 	}
> 
>  Unlock:

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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