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

Wu Fengguang
2009-05-05T02:24:27Z

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.

+ error = memory_bm_create(&orig_bm, GFP_IMAGE, PG_ANY);
+ if (error)
+ goto err_out;
+
+ error = memory_bm_create(&copy_bm, GFP_IMAGE, PG_ANY);
+ if (error)
+ goto err_out;

memory_bm_create() is called a number of times, each time it will
call create_mem_extents()/memory_bm_free(). Can they be optimized to
be called only once?

A side note: there are somehow duplicated *_extent_*() logics in the
filesystems, is it possible that we abstract out some of the common code?

+ for_each_populated_zone(zone) {
+ size += snapshot_additional_pages(zone);
+ count += zone_page_state(zone, NR_FREE_PAGES);
+ if (!is_highmem(zone))
+ count -= zone->lowmem_reserve[ZONE_NORMAL];
+ }

Why [ZONE_NORMAL] instead of [zone]? ZONE_NORMAL may not always be the largest zone,
for example, My 4GB laptop has a tiny ZONE_NORMAL and a large ZONE_DMA32.

+ /* If size < max_size, preallocating enough memory may be impossible. */
+ if (count > 0 && size == max_size)
+ error = -ENOMEM;
+ if (error)
+ goto err_out;

The two if()s can be merged.

At last, I'd express my major concern about the transition to preallocate
based memory shrinking: will it lead to more random swapping IOs?

Thanks,
Fengguang