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SubjectRe: [PATCH 5/5] PM/Hibernate: Do not release preallocated memory unnecessarily (rev. 2)
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@sisk.pl>
> >
> > 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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