Message-Id: <201105151151.26745.rjw@sisk.pl>
Date:	Sun, 15 May 2011 11:51:26 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Martin Steigerwald <Martin@...htvoll.de>
Cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM / Hibernate: Add sysfs knob to control size of memory for drivers

On Sunday, May 15, 2011, Rafael J. Wysocki wrote:
> On Sunday, May 15, 2011, Martin Steigerwald wrote:
> > Am Sonntag, 15. Mai 2011 schrieb Rafael J. Wysocki:
> > > Hi,
> > 
> > Hi Rafael,
> 
> Hi,
> 
> > > On Tuesday, May 10, 2011, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > > 
> > > > Martin reports that on his system hibernation occasionally fails due
> > > > to the lack of memory, because the radeon driver apparently allocates
> > > > too much of it during the device freeze stage.  It turns out that the
> > > > amount of memory allocated by radeon during hibernation (and
> > > > presumably during system suspend too) depends on the utilization of
> > > > the GPU (e.g. hibernating while there are two KDE 4 sessions with
> > > > compositing enabled causes radeon to allocate more memory than for
> > > > one KDE 4 session).
> > > > 
> > > > In principle it should be possible to use image_size to make the
> > > > memory preallocation mechanism free enough memory for the radeon
> > > > driver, but in practice it is not easy to guess the right value
> > > > because of the way the preallocation code uses image_size.  For this
> > > > reason, it seems reasonable to allow users to control the amount of
> > > > memory reserved for driver allocations made after the preallocation,
> > > > which currently is constant and amounts to 1 MB.
> > > > 
> > > > Introduce a new sysfs file, /sys/power/reserved_size, whose value
> > > > will be used as the amount of memory to reserve for the
> > > > post-preallocation reservations made by device drivers, in bytes.
> > > > For backwards compatibility, set its default (and initial) value to
> > > > the currently used number (1 MB).
> > > > 
> > > > References: https://bugzilla.kernel.org/show_bug.cgi?id=34102
> > > > Reported-by: Martin Steigerwald <Martin@...htvoll.de>
> > > > Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> > > 
> > > OK, there are no comments, so my understanding is that everyone is fine
> > > with this patch and I can add it to my linux-next branch.
> > 
> > Extensively
> > 
> > Tested-by: Martin Steigerwald <Martin@...htvoll.de>
> > 
> > This patch makes a complete difference for me. Instead of not knowing 
> > whether my ThinkPad T42 will hibernate with lots of applications open and 
> > thus closing applications prior to hibernation preventively now it simply 
> > will. *Always*.
> > 
> > I even tested it with two KDE 4 sessions with running desktop search 
> > indexing on one. It took ages, cause KDE 4.6 desktop search / nepomuk stuff 
> > seems to I/O load the machine beyond anything (bugs reported there), but 
> > it worked.
> > 
> > 16 MiB reserved_size has been enough for one KDE session. With 128 MiB the 
> > linux kernel hibernated two KDE sessions.
> > 
> > Drivers allocating their memory via suspend/hibernate notifiers according 
> > to Rafael should fix the root cause, but until that is done, this will do. 
> > Adjusting imagesize instead never gave me such a reliable result.
> 
> In fact, if drivers allocated their memory from suspend/hibernate notifiers,
> that would be practically equivalent to setting reserved_size to the total
> amount of memory reserved by the drivers.  However, it may be difficult
> for drivers to predict how much memory they will need at the time the
> notifiers are called (they are called before freezing user space).
> 
> Thus I'm considering a change that will cause device drivers' ->prepare()
> callbacks to be executed before the preallocation of memory takes place.
> In that case the drivers may allocate memory from their ->prepare()
> callbacks _after_ user space has been frozen and that will make more
> sense overall.
> 
> For now, however, I think that exposing reserved_size is the right choice.

BTW, I'm going to add the appended patch on top of it.

Thanks,
Rafael

---
Author: Rafael J. Wysocki <rjw@...k.pl>
Date:   Sun May 15 11:39:48 2011 +0200

    Revert "PM / Hibernate: Reduce autotuned default image size"
    
    This reverts commit bea3864fb627d110933cfb8babe048b63c4fc76e
    (PM / Hibernate: Reduce autotuned default image size), because users
    are now able to resolve the issue this commit was supposed to address
    in a different way (i.e. by using the new /sys/power/reserved_size
    interface).
    
    Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index d69e332..ace5588 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -54,15 +54,15 @@ void __init hibernate_reserved_size_init(void)
 
 /*
  * Preferred image size in bytes (tunable via /sys/power/image_size).
- * When it is set to N, the image creating code will do its best to
- * ensure the image size will not exceed N bytes, but if that is
- * impossible, it will try to create the smallest image possible.
+ * When it is set to N, swsusp will do its best to ensure the image
+ * size will not exceed N bytes, but if that is impossible, it will
+ * try to create the smallest image possible.
  */
 unsigned long image_size;
 
 void __init hibernate_image_size_init(void)
 {
-	image_size = (totalram_pages / 3) * PAGE_SIZE;
+	image_size = ((totalram_pages * 2) / 5) * PAGE_SIZE;
 }
 
 /* List of PBEs needed for restoring the pages that were allocated before
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