Re: [PATCH 05/22] Hibernation: Switch to preallocating swap.

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Saturday, September 25, 2010, Nigel Cunningham wrote:
> Switch from allocating swap as the image is written to allocating
> storage prior to writing the image.

Hmm, I think I know what the patch does, but I don't really understand the
changelog.  Care to explain/fix?

Thanks,
Rafael


> Signed-off-by: Nigel Cunningham <nigel@tuxonice.net>
> ---
>  kernel/power/swap.c |   62 ++++++++++++++++++++++++++++++--------------------
>  1 files changed, 37 insertions(+), 25 deletions(-)
> 
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index cebf91c..bebd2cf 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -202,6 +202,33 @@ int alloc_swapdev_blocks(int needed)
>  }
>  
>  /**
> + *	allocate_swap - Allocate enough swap to save the image.
> + *
> + *	Calculates the number of swap pages actually needed and seeks
> + *	to allocate that many from the resume partition. Returns TRUE
> + *	or FALSE to indicate whether we got enough storage.
> + */
> +
> +static int allocate_swap(unsigned int nr_pages)
> +{
> +	unsigned int free_swap = count_swap_pages(root_swap, 1);
> +
> +	nr_pages += DIV_ROUND_UP(nr_pages, MAP_PAGE_ENTRIES);
> +
> +	pr_debug("PM: Free swap pages: %u\n", free_swap);
> +	if (free_swap < nr_pages)
> +		return 0;
> +
> +	if (alloc_swapdev_blocks(nr_pages) < nr_pages) {
> +		free_all_swap_pages(root_swap);
> +		return 0;
> +	}
> +
> +	reset_storage_pos();
> +	return 1;
> +}
> +
> +/**
>   *	free_all_swap_pages - free swap pages allocated for saving image data.
>   *	It also frees the extents used to register which swap entries had been
>   *	allocated.
> @@ -324,7 +351,7 @@ static void release_swap_writer(struct swap_map_handle *handle)
>  	handle->cur = NULL;
>  }
>  
> -static int get_swap_writer(struct swap_map_handle *handle)
> +static int get_swap_writer(struct swap_map_handle *handle, unsigned long pages)
>  {
>  	int ret;
>  
> @@ -340,7 +367,12 @@ static int get_swap_writer(struct swap_map_handle *handle)
>  		ret = -ENOMEM;
>  		goto err_close;
>  	}
> -	handle->cur_swap = alloc_swapdev_block(root_swap);
> +	if (!allocate_swap(pages)) {
> +		printk(KERN_ERR "PM: Not enough free swap\n");
> +		ret = -ENOSPC;
> +		goto err_close;
> +	}
> +	handle->cur_swap = next_swapdev_block();
>  	if (!handle->cur_swap) {
>  		ret = -ENOSPC;
>  		goto err_rel;
> @@ -363,7 +395,7 @@ static int swap_write_page(struct swap_map_handle *handle, void *buf,
>  
>  	if (!handle->cur)
>  		return -EINVAL;
> -	offset = alloc_swapdev_block(root_swap);
> +	offset = next_swapdev_block();
>  	error = write_page(buf, offset, bio_chain);
>  	if (error)
>  		return error;
> @@ -372,7 +404,7 @@ static int swap_write_page(struct swap_map_handle *handle, void *buf,
>  		error = hib_wait_on_bio_chain(bio_chain);
>  		if (error)
>  			goto out;
> -		offset = alloc_swapdev_block(root_swap);
> +		offset = next_swapdev_block();
>  		if (!offset)
>  			return -ENOSPC;
>  		handle->cur->next_swap = offset;
> @@ -463,21 +495,6 @@ static int save_image(struct swap_map_handle *handle,
>  }
>  
>  /**
> - *	enough_swap - Make sure we have enough swap to save the image.
> - *
> - *	Returns TRUE or FALSE after checking the total amount of swap
> - *	space avaiable from the resume partition.
> - */
> -
> -static int enough_swap(unsigned int nr_pages)
> -{
> -	unsigned int free_swap = count_swap_pages(root_swap, 1);
> -
> -	pr_debug("PM: Free swap pages: %u\n", free_swap);
> -	return free_swap > nr_pages + PAGES_FOR_IO;
> -}
> -
> -/**
>   *	swsusp_write - Write entire image and metadata.
>   *	@flags: flags to pass to the "boot" kernel in the image header
>   *
> @@ -496,16 +513,11 @@ int swsusp_write(unsigned int flags)
>  	int error;
>  
>  	pages = snapshot_get_image_size();
> -	error = get_swap_writer(&handle);
> +	error = get_swap_writer(&handle, pages);
>  	if (error) {
>  		printk(KERN_ERR "PM: Cannot get swap writer\n");
>  		return error;
>  	}
> -	if (!enough_swap(pages)) {
> -		printk(KERN_ERR "PM: Not enough free swap\n");
> -		error = -ENOSPC;
> -		goto out_finish;
> -	}
>  	memset(&snapshot, 0, sizeof(struct snapshot_handle));
>  	error = snapshot_read_next(&snapshot);
>  	if (error < PAGE_SIZE) {
>