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

[Wu Fengguang]

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@xxxxxxx>
> > 
> > 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,
Fengguang
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