Re: [PATCH 4/6] PM/Hibernate: Rework shrinking of memory

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Thursday 14 May 2009, Pavel Machek wrote:
> 
> > > > > The main point (I thought) was to remove shrink_all_memory().  Instead,
> > > > > we're retaining it and adding even more stuff?
> > > > 
> > > > The idea is that afterwards we can drop shrink_all_memory() once the
> > > > performance problem has been resolved.  Also, we now allocate memory for the
> > > > image using GFP_KERNEL instead of doing it with GFP_ATOMIC after freezing
> > > > devices.  I'd think that's an improvement?
> > > 
> > > Dunno.  GFP_KERNEL might attempt to do writeback/swapout/etc, which
> > > could be embarrassing if the devices are frozen.
> > 
> > They aren't, because the preallocation is done upfront, so once the OOM killer
> > has been taken care of, it's totally safe. :-)
> 
> As is GFP_ATOMIC. Except that GFP_KERNEL will cause catastrophic
> consequences when accounting goes wrong. (New kernel's idea of what is
> on disk will differ from what is _really_ on disk.)
> 
> If accounting is right, GFP_ATOMIC and GFP_KERNEL is equivalent.
> 
> If accounting is wrong, GFP_ATOMIC will fail with NULL, while
> GFP_KERNEL will do something bad.
> 
> I'd keep GFP_ATOMIC (or GFP_NOIO or similar). 

Repeating myself: with this and the next patch applied, we preallocate memory
for the image _before_ freezing devices and therefore it is safe to use
GFP_KERNEL, because the OOM killer has been taken care of by [3/6].

Thanks,
Rafael

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