Re: [PATCH 5/5] PM/Hibernate: Do not release preallocated memory unnecessarily (rev. 2)

Wu Fengguang
2009-05-05T23:40:56Z

On Wed, May 06, 2009 at 07:07:44AM +0800, Rafael J. Wysocki wrote:
> On Tuesday 05 May 2009, Wu Fengguang wrote:
> > On Tue, May 05, 2009 at 10:24:27AM +0800, Wu Fengguang wrote:
> > > On Mon, May 04, 2009 at 08:22:38AM +0800, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rjw-KKrjLPT3xs0@public.gmane.org>
> > > >
> > > > Since the hibernation code is now going to use allocations of memory
> > > > to create enough room for the image, it can also use the page frames
> > > > allocated at this stage as image page frames. The low-level
> > > > hibernation code needs to be rearranged for this purpose, but it
> > > > allows us to avoid freeing a great number of pages and allocating
> > > > these same pages once again later, so it generally is worth doing.
> > > >
> > > > [rev. 2: Change the strategy of preallocating memory to allocate as
> > > > many pages as needed to get the right image size in one shot (the
> > > > excessive allocated pages are released afterwards).]
> > >
> > > Rafael, I tried out your patches and found doubled memory shrink speed!
> > >
> > > [ 579.641781] PM: Preallocating image memory ... done (allocated 383900 pages, 128000 image pages kept)
> > > [ 583.087875] PM: Allocated 1535600 kbytes in 3.43 seconds (447.69 MB/s)
> >
> > > For you reference, here is the free memory before/after
> > > hibernate_preallocate_memory():
> > >
> > > # free
> > > total used free shared buffers cached
> > > Mem: 1933 1917 15 0 0 1845
> > > -/+ buffers/cache: 72 1861
> > > Swap: 0 0 0
> > >
> > > # free
> > > total used free shared buffers cached
> > > Mem: 1933 920 1012 0 0 356
> > > -/+ buffers/cache: 563 1369
> > > Swap: 0 0 0
> > >
> > > It seems that the preallocated memory is not freed on -ENOMEM.
> >
> > Ah, this was my fault.
> >
> > I used to do this debugging trick:
> >
> > @@ -1207,7 +1207,7 @@ int hibernate_preallocate_memory(void)
> > pages, size);
> > swsusp_show_speed(&start, &stop, pages, "Allocated");
> >
> > - return 0;
> > + return -ENOMEM;
> >
> > err_out:
> > printk(KERN_CONT "\n");
> >
> > That "return -ENOMEM" should be "error = -ENOMEM" :-)
> >
> > Here is one more run:
> >
> > [ 194.016991] PM: Preallocating image memory ... done (allocated 383897 pages, 128000 image pages kept)
> > [ 196.505999] PM: Allocated 1535588 kbytes in 2.47 seconds (621.69 MB/s)
> >
> > Now the free report is back to normal:
> >
> > # free
> > total used free shared buffers cached
> > Mem: 1933 74 1858 0 0 15

The above 'free' still exposed something wrong: only 74M memory are left,
instead of image_size=500M memory. I'm prepared to test your updated patches :-)