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

Rafael J. Wysocki
2009-05-05T23:07:44Z

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

Thanks for testing. The results look encouraging, but I'd also like to get rid
of the regression mentioned in my previous message.

Thanks,
Rafael