linux-kernel - [PATCH v8]: Hibernation: lower/better control the amount of pages used for buffering

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Message-ID: <1333418527.2035.11.camel@shrek.rexursive.com>
Date:	Tue, 03 Apr 2012 12:02:07 +1000
From:	Bojan Smojver <bojan@...ursive.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH v8]: Hibernation: lower/better control the amount of pages
 used for buffering

Hi Rafael,

Here is another version of the same, this time with a hint of
super-paranoia. The only change when compared to v7 is the test of free
pages v. required free pages. This version will trigger BIO chain flush
on less or equal, instead of just on less. Just in case required free
pages becomes zero in the calculations.

---------------------------------------
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@...ursive.com>
---
 kernel/power/swap.c |   35 ++++++++++++++++++++++++-----------
 1 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index 8742fd0..26d304b 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -6,7 +6,7 @@
  *
  * Copyright (C) 1998,2001-2005 Pavel Machek <pavel@....cz>
  * Copyright (C) 2006 Rafael J. Wysocki <rjw@...k.pl>
- * Copyright (C) 2010 Bojan Smojver <bojan@...ursive.com>
+ * Copyright (C) 2010-2012 Bojan Smojver <bojan@...ursive.com>
  *
  * This file is released under the GPLv2.
  *
@@ -51,6 +51,15 @@
 
 #define MAP_PAGE_ENTRIES	(PAGE_SIZE / sizeof(sector_t) - 1)
 
+/*
+ * Number of pages required to be kept free while writing the image. Always
+ * three quarters of all available pages before the writing starts.
+ */
+static inline unsigned long reqd_free_pages(void)
+{
+	return (nr_free_pages() / 4) * 3;
+}
+
 struct swap_map_page {
 	sector_t entries[MAP_PAGE_ENTRIES];
 	sector_t next_swap;
@@ -72,7 +81,7 @@ 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 +325,7 @@ 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 = reqd_free_pages();
 	handle->first_sector = handle->cur_swap;
 	return 0;
 err_rel:
@@ -352,11 +360,15 @@ 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 = reqd_free_pages();
 	}
  out:
 	return error;
@@ -404,7 +416,7 @@ 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 +627,10 @@ 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 = reqd_free_pages();
 
 	/*
 	 * Start the CRC32 thread.
@@ -1129,8 +1141,9 @@ 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()) / 4;
 	read_pages = clamp_val(read_pages, LZO_CMP_PAGES, LZO_READ_PAGES);
 
 	for (i = 0; i < read_pages; i++) {
---------------------------------------

-- 
Bojan

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