[PATCH v4]: Hibernation: lower/better control the amount of pages used for buffering

[PATCH v4]: Hibernation: lower/better control the amount of pages used for buffering

[Bojan Smojver]

Hi Rafael,

One more version. This time we require that 3/4 of pages be available
when writing the image, otherwise we flush. Just erring on the side of
caution. Otherwise the same as v3.

---------------------------------------
Hibernation/thaw improvements:

1. Set maximum number of pages for read buffering consistently, instead
of inadvertently depending on the size of the sector type.

2. Use at most one quarter of free pages for read buffering.

3. Require that number of free pages when writing the image never falls
below three quarters of total free pages available.

Signed-off-by: Bojan Smojver <bojan@rexursive.com>
---
 kernel/power/swap.c |   26 +++++++++++++++-----------
 1 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index 8742fd0..b06fed3 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -6,7 +6,7 @@
  *
  * Copyright (C) 1998,2001-2005 Pavel Machek <pavel@ucw.cz>
  * Copyright (C) 2006 Rafael J. Wysocki <rjw@sisk.pl>
- * Copyright (C) 2010 Bojan Smojver <bojan@rexursive.com>
+ * Copyright (C) 2010-2012 Bojan Smojver <bojan@rexursive.com>
  *
  * This file is released under the GPLv2.
  *
@@ -72,7 +72,7 @@ struct swap_map_handle {
 	sector_t cur_swap;
 	sector_t first_sector;
 	unsigned int k;
-	unsigned long nr_free_pages, written;
+	unsigned long reqd_free_pages;
 	u32 crc32;
 };
 
@@ -316,8 +316,7 @@ static int get_swap_writer(struct swap_map_handle *handle)
 		goto err_rel;
 	}
 	handle->k = 0;
-	handle->nr_free_pages = nr_free_pages() >> 1;
-	handle->written = 0;
+	handle->reqd_free_pages = (nr_free_pages() >> 2) * 3;
 	handle->first_sector = handle->cur_swap;
 	return 0;
 err_rel:
@@ -352,11 +351,15 @@ static int swap_write_page(struct swap_map_handle *handle, void *buf,
 		handle->cur_swap = offset;
 		handle->k = 0;
 	}
-	if (bio_chain && ++handle->written > handle->nr_free_pages) {
+	if (bio_chain && nr_free_pages() < handle->reqd_free_pages) {
 		error = hib_wait_on_bio_chain(bio_chain);
 		if (error)
 			goto out;
-		handle->written = 0;
+		/*
+		 * Recalculate the number of required free pages, to make sure
+		 * we never take more than a quarter.
+		 */
+		handle->reqd_free_pages = (nr_free_pages() >> 2) * 3;
 	}
  out:
 	return error;
@@ -404,7 +407,7 @@ static int swap_writer_finish(struct swap_map_handle *handle,
 #define LZO_THREADS	3
 
 /* Maximum number of pages for read buffering. */
-#define LZO_READ_PAGES	(MAP_PAGE_ENTRIES * 8)
+#define LZO_READ_PAGES	8192
 
 
 /**
@@ -615,10 +618,10 @@ static int save_image_lzo(struct swap_map_handle *handle,
 	}
 
 	/*
-	 * Adjust number of free pages after all allocations have been done.
-	 * We don't want to run out of pages when writing.
+	 * Adjust the number of required free pages after all allocations have
+	 * been done. We don't want to run out of pages when writing.
 	 */
-	handle->nr_free_pages = nr_free_pages() >> 1;
+	handle->reqd_free_pages = (nr_free_pages() >> 2) * 3;
 
 	/*
 	 * Start the CRC32 thread.
@@ -1129,8 +1132,9 @@ static int load_image_lzo(struct swap_map_handle *handle,
 
 	/*
 	 * Adjust number of pages for read buffering, in case we are short.
+	 * Never take more than a quarter of all available pages.
 	 */
-	read_pages = (nr_free_pages() - snapshot_get_image_size()) >> 1;
+	read_pages = (nr_free_pages() - snapshot_get_image_size()) >> 2;
 	read_pages = clamp_val(read_pages, LZO_CMP_PAGES, LZO_READ_PAGES);
 
 	for (i = 0; i < read_pages; i++) {
---------------------------------------

-- 
Bojan

Re: [PATCH v4]: Hibernation: lower/better control the amount of pages used for buffering

[Rafael J. Wysocki]

On Friday, March 23, 2012, Bojan Smojver wrote:
> Hi Rafael,
> 
> One more version. This time we require that 3/4 of pages be available
> when writing the image, otherwise we flush. Just erring on the side of
> caution. Otherwise the same as v3.
> 
> ---------------------------------------
> Hibernation/thaw improvements:
> 
> 1. Set maximum number of pages for read buffering consistently, instead
> of inadvertently depending on the size of the sector type.
> 
> 2. Use at most one quarter of free pages for read buffering.
> 
> 3. Require that number of free pages when writing the image never falls
> below three quarters of total free pages available.
> 
> Signed-off-by: Bojan Smojver <bojan@rexursive.com>
> ---
>  kernel/power/swap.c |   26 +++++++++++++++-----------
>  1 files changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 8742fd0..b06fed3 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -6,7 +6,7 @@
>   *
>   * Copyright (C) 1998,2001-2005 Pavel Machek <pavel@ucw.cz>
>   * Copyright (C) 2006 Rafael J. Wysocki <rjw@sisk.pl>
> - * Copyright (C) 2010 Bojan Smojver <bojan@rexursive.com>
> + * Copyright (C) 2010-2012 Bojan Smojver <bojan@rexursive.com>
>   *
>   * This file is released under the GPLv2.
>   *
> @@ -72,7 +72,7 @@ struct swap_map_handle {
>  	sector_t cur_swap;
>  	sector_t first_sector;
>  	unsigned int k;
> -	unsigned long nr_free_pages, written;
> +	unsigned long reqd_free_pages;
>  	u32 crc32;
>  };
>  
> @@ -316,8 +316,7 @@ static int get_swap_writer(struct swap_map_handle *handle)
>  		goto err_rel;
>  	}
>  	handle->k = 0;
> -	handle->nr_free_pages = nr_free_pages() >> 1;
> -	handle->written = 0;
> +	handle->reqd_free_pages = (nr_free_pages() >> 2) * 3;

This computation is done in three different places in the same way.
Perhaps create a macro or a static inline function for that?

Also, I'm not sure if the microoptimization here actually helps a lot.
The compiler should be smart enough to optimize that properly.  So, I'd just
write (nr_free_pages() / 4) * 3 whose meaning is much more obvious. :-)

Apart from this, looks good.

Thanks,
Rafael


>  	handle->first_sector = handle->cur_swap;
>  	return 0;
>  err_rel:
> @@ -352,11 +351,15 @@ static int swap_write_page(struct swap_map_handle *handle, void *buf,
>  		handle->cur_swap = offset;
>  		handle->k = 0;
>  	}
> -	if (bio_chain && ++handle->written > handle->nr_free_pages) {
> +	if (bio_chain && nr_free_pages() < handle->reqd_free_pages) {
>  		error = hib_wait_on_bio_chain(bio_chain);
>  		if (error)
>  			goto out;
> -		handle->written = 0;
> +		/*
> +		 * Recalculate the number of required free pages, to make sure
> +		 * we never take more than a quarter.
> +		 */
> +		handle->reqd_free_pages = (nr_free_pages() >> 2) * 3;
>  	}
>   out:
>  	return error;
> @@ -404,7 +407,7 @@ static int swap_writer_finish(struct swap_map_handle *handle,
>  #define LZO_THREADS	3
>  
>  /* Maximum number of pages for read buffering. */
> -#define LZO_READ_PAGES	(MAP_PAGE_ENTRIES * 8)
> +#define LZO_READ_PAGES	8192
>  
>  
>  /**
> @@ -615,10 +618,10 @@ static int save_image_lzo(struct swap_map_handle *handle,
>  	}
>  
>  	/*
> -	 * Adjust number of free pages after all allocations have been done.
> -	 * We don't want to run out of pages when writing.
> +	 * Adjust the number of required free pages after all allocations have
> +	 * been done. We don't want to run out of pages when writing.
>  	 */
> -	handle->nr_free_pages = nr_free_pages() >> 1;
> +	handle->reqd_free_pages = (nr_free_pages() >> 2) * 3;
>  
>  	/*
>  	 * Start the CRC32 thread.
> @@ -1129,8 +1132,9 @@ static int load_image_lzo(struct swap_map_handle *handle,
>  
>  	/*
>  	 * Adjust number of pages for read buffering, in case we are short.
> +	 * Never take more than a quarter of all available pages.
>  	 */
> -	read_pages = (nr_free_pages() - snapshot_get_image_size()) >> 1;
> +	read_pages = (nr_free_pages() - snapshot_get_image_size()) >> 2;
>  	read_pages = clamp_val(read_pages, LZO_CMP_PAGES, LZO_READ_PAGES);
>  
>  	for (i = 0; i < read_pages; i++) {
> ---------------------------------------
> 
>