Re: [RFC][PATCH 4/5] PM/Hibernate: Rework shrinking of memory

[Nigel Cunningham]

Hi.

On Thu, 2009-05-07 at 00:44 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@xxxxxxx>
> 
> Rework swsusp_shrink_memory() so that it calls shrink_all_memory()
> just once to make some room for the image and then allocates memory
> to apply more pressure to the memory management subsystem, if
> necessary.
> 
> Unfortunately, we don't seem to be able to drop shrink_all_memory()
> entirely just yet, because that would lead to huge performance
> regressions in some test cases.

I know it doesn't fit with your current way of doing things, but have
you considered trying larger order allocations as a means of getting
memory freed? I have code in tuxonice_prepare_image.c (look for
extra_pages_allocated) that might be helpful for this purpose.

> Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> ---
>  kernel/power/snapshot.c |  145 ++++++++++++++++++++++++++++++++----------------
>  1 file changed, 98 insertions(+), 47 deletions(-)
> 
> Index: linux-2.6/kernel/power/snapshot.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/snapshot.c
> +++ linux-2.6/kernel/power/snapshot.c
> @@ -1066,69 +1066,120 @@ void swsusp_free(void)
>  	buffer = NULL;
>  }
>  
> +/* Helper functions used for the shrinking of memory. */
> +
>  /**
> - *	swsusp_shrink_memory -  Try to free as much memory as needed
> - *
> - *	... but do not OOM-kill anyone
> + * preallocate_image_memory - Allocate given number of page frames
> + * @nr_pages: Number of page frames to allocate
>   *
> - *	Notice: all userland should be stopped before it is called, or
> - *	livelock is possible.
> + * Return value: Number of page frames actually allocated
>   */
> -
> -#define SHRINK_BITE	10000
> -static inline unsigned long __shrink_memory(long tmp)
> +static unsigned long preallocate_image_memory(unsigned long nr_pages)
>  {
> -	if (tmp > SHRINK_BITE)
> -		tmp = SHRINK_BITE;
> -	return shrink_all_memory(tmp);
> +	unsigned long nr_alloc = 0;
> +
> +	while (nr_pages-- > 0) {
> +		struct page *page;
> +
> +		page = alloc_image_page(GFP_KERNEL | __GFP_NOWARN);

Ah... now I see you're using __GFP_NOWARN already :)

> +		if (!page)
> +			break;
> +		nr_alloc++;
> +	}
> +
> +	return nr_alloc;
>  }
>  
> +/**
> + * swsusp_shrink_memory -  Make the kernel release as much memory as needed
> + *
> + * To create a hibernation image it is necessary to make a copy of every page
> + * frame in use.  We also need a number of page frames to be free during
> + * hibernation for allocations made while saving the image and for device
> + * drivers, in case they need to allocate memory from their hibernation
> + * callbacks (these two numbers are given by PAGES_FOR_IO and SPARE_PAGES,
> + * respectively, both of which are rough estimates).  To make this happen, we
> + * compute the total number of available page frames and allocate at least
> + *
> + * ([page frames total] + PAGES_FOR_IO + [metadata pages]) / 2 + 2 * SPARE_PAGES
> + *
> + * of them, which corresponds to the maximum size of a hibernation image.
> + *
> + * If image_size is set below the number following from the above formula,
> + * the preallocation of memory is continued until the total number of page
> + * frames in use is below the requested image size or it is impossible to
> + * allocate more memory, whichever happens first.
> + */

You should also be taking into account how much storage is available
here - that would make things more reliable. If compression is begin
used, you could also apply an 'expected compression ratio' so that you
don't unnecessarily free memory that will fit once compressed.

>  int swsusp_shrink_memory(void)
>  {
> -	long tmp;
>  	struct zone *zone;
> -	unsigned long pages = 0;
> -	unsigned int i = 0;
> -	char *p = "-\\|/";
> +	unsigned long saveable, size, max_size, count, pages = 0;
>  	struct timeval start, stop;
> +	int error = 0;
>  
> -	printk(KERN_INFO "PM: Shrinking memory...  ");
> +	printk(KERN_INFO "PM: Shrinking memory ... ");

Without the space is normal, at least to my mind.

>  	do_gettimeofday(&start);
> -	do {
> -		long size, highmem_size;
>  
> -		highmem_size = count_highmem_pages();
> -		size = count_data_pages() + PAGES_FOR_IO + SPARE_PAGES;
> -		tmp = size;
> -		size += highmem_size;
> -		for_each_populated_zone(zone) {
> -			tmp += snapshot_additional_pages(zone);
> -			if (is_highmem(zone)) {
> -				highmem_size -=
> -					zone_page_state(zone, NR_FREE_PAGES);
> -			} else {
> -				tmp -= zone_page_state(zone, NR_FREE_PAGES);
> -				tmp += zone->lowmem_reserve[ZONE_NORMAL];
> -			}
> -		}
> +	/* Count the number of saveable data pages. */
> +	saveable = count_data_pages() + count_highmem_pages();
> +
> +	/*
> +	 * Compute the total number of page frames we can use (count) and the
> +	 * number of pages needed for image metadata (size).
> +	 */
> +	count = saveable;
> +	size = 0;
> +	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];
> +	}
>  
> -		if (highmem_size < 0)
> -			highmem_size = 0;

You're not taking watermarks into account here - that isn't a problem
with shrink_all_memory because it usually frees more than you ask for
(or has done in the past), but if you're getting exactly what you ask
for, you might run into trouble if more than half of memory is in use to
start with.

> +	/* Compute the maximum number of saveable pages to leave in memory. */
> +	max_size = (count - (size + PAGES_FOR_IO)) / 2 - 2 * SPARE_PAGES;
> +	size = DIV_ROUND_UP(image_size, PAGE_SIZE);
> +	if (size > max_size)
> +		size = max_size;
> +	/*
> +	 * If the maximum is not lesser than the current number of saveable

s/lesser/less/

> +	 * pages in memory, we don't need to do anything more.
> +	 */
> +	if (size >= saveable)
> +		goto out;
>  
> -		tmp += highmem_size;
> -		if (tmp > 0) {
> -			tmp = __shrink_memory(tmp);
> -			if (!tmp)
> -				return -ENOMEM;
> -			pages += tmp;
> -		} else if (size > image_size / PAGE_SIZE) {
> -			tmp = __shrink_memory(size - (image_size / PAGE_SIZE));
> -			pages += tmp;
> -		}
> -		printk("\b%c", p[i++%4]);
> -	} while (tmp > 0);
> +	/*
> +	 * Let the memory management subsystem know that we're going to need a
> +	 * large number of page frames to allocate and make it free some memory.
> +	 * NOTE: If this is not done, performance is heavily affected in some
> +	 * test cases.
> +	 */
> +	shrink_all_memory(saveable - size);
> +
> +	/*
> +	 * The number of saveable pages in memory was too high, so apply some
> +	 * pressure to decrease it.  First, make room for the largest possible
> +	 * image and fail if that doesn't work.  Next, try to decrease the size
> +	 * of the image as much as indicated by image_size.
> +	 */
> +	count -= max_size;
> +	pages = preallocate_image_memory(count);
> +	if (pages < count)
> +		error = -ENOMEM;
> +	else
> +		pages += preallocate_image_memory(max_size - size);
> +
> +	/* Release all of the preallocated page frames. */
> +	swsusp_free();
> +
> +	if (error) {
> +		printk(KERN_CONT "\n");
> +		return error;
> +	}
> +
> + out:
>  	do_gettimeofday(&stop);
> -	printk("\bdone (%lu pages freed)\n", pages);
> +	printk(KERN_CONT "done (preallocated %lu free pages)\n", pages);
>  	swsusp_show_speed(&start, &stop, pages, "Freed");
>  
>  	return 0;

Regards,

Nigel

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