On Wed, 13 May 2009 22:55:03 +0200
"Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> On Wednesday 13 May 2009, Andrew Morton wrote:
> > On Wed, 13 May 2009 10:39:25 +0200
> > "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
> >
> > > From: Rafael J. Wysocki <rjw@xxxxxxx>
> > >
> > > Rework swsusp_shrink_memory() so that it calls shrink_all_memory()
> > > just once to make some room for the image and then allocates memory
> > > to apply more pressure to the memory management subsystem, if
> > > necessary.
> > >
> > > Unfortunately, we don't seem to be able to drop shrink_all_memory()
> > > entirely just yet, because that would lead to huge performance
> > > regressions in some test cases.
> > >
> >
> > Isn't this a somewhat large problem?
>
> Yes, it is. The thing is 8 times slower (15 s vs 2 s) without the
> shrink_all_memory() in at least one test case. 100% reproducible.
erk. Any ideas why? A quick peek at a kernel profile and perhaps
the before-and-after delta in the /proc/vmstat numbers would probably
guide us there.
> > 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. GFP_NOIO sounds
appropriate.
> > > +{
> > > + unsigned long ratio = (numerator << FRACTION_SHIFT) / denominator;
> > >
> > > -#define SHRINK_BITE 10000
> > > -static inline unsigned long __shrink_memory(long tmp)
> > > + x *= ratio;
> > > + return x >> FRACTION_SHIFT;
> > > +}
> >
> > Strange function. Would it not be simpler/clearer to do it with 64-bit
> > scalars, multiplication and do_div()?
>
> Sure, I can do it this way too. Is it fine to use u64 for this purpose?
I suppose so. All/most of the implementations of do_div() are done as
macros so it's pretty hard to work out what the types are. But
do_div() does expect a u64 rather than `unsigned long long'.
_______________________________________________
linux-pm mailing list
linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/linux-pm
