[PATCH v2] PM/hibernation: set the default image size for large memory

[Xueqin Luo]

From: xueqin Luo <luoxueqin@xxxxxxxxxx>

As computers have more and more memory, they can store larger and
larger images. This poses a problem. Let's take a 16GB computer as
an example. When the number of pre-allocated pages is greater than
900,000 and smaller than image_size, the duration of S4 increases
with the number of saved pages. When the number of pre-allocated
pages reaches 1.2 million, the duration of S4 increases by 8-10s.

We found that the image size is generally more than 900,000 pages,
so we set the default size of image_size for 16GB and above
computers to 1 million pages, which can reduce the running time
of S4 under certain conditions.

This is the test data for 5 hours after the computer is turned on:

Original kernel begin:

[2023-02-24 19:16:56] [   46.105423][ 2] [ T3075] PM: hibernation entry
[2023-02-24 19:16:59] [   47.632000][ 1] [ T3075] done (allocated 
959239 pages)
[2023-02-24 19:18:05] [   56.987043][ 2] [ T3075] PM: hibernation exit

Five hours later:

[2023-02-25 00:22:48] [18069.651640][ 4] [ T7590] PM: hibernation entry
[2023-02-25 01:23:59] [21671.194049][ 0] [ T8563] done (allocated 
1228878 pages)
[2023-02-25 00:24:06] [18080.639889][ 2] [ T7590] PM: hibernation exit

After 5h, you can see that the S4 takes 8s more time.

Five hours later, the modified kernel test data:

[2023-02-24 15:52:08] [18190.171183][ 7] [T11151] PM: hibernation entry
[2023-02-24 15:52:11] [18191.677021][ 7] [T11151] done (allocated 
792597 pages)
[2023-02-24 15:53:15] [18201.028488][ 2] [T11151] PM: hibernation exit

You can see that after five hours, the time has changed little compared 
to the initial test data.

Signed-off-by: xueqin Luo <luoxueqin@xxxxxxxxxx>
---

v3: modify some comments

v2: add test data

 kernel/power/snapshot.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index cd8b7b35f1e8..fa3950b19849 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -136,7 +136,14 @@ unsigned long image_size;
 
 void __init hibernate_image_size_init(void)
 {
-	image_size = ((totalram_pages() * 2) / 5) * PAGE_SIZE;
+	/* The totalram pages() for a computer of 16 memory size is
+	 * equal to 4032990 pages. And according to our observation,
+	 * the average image size is less than 1 million pages.
+	 */
+	if (totalram_pages() < 4032990)
+		image_size = ((totalram_pages() * 2) / 5) * PAGE_SIZE;
+	else
+		image_size = 1000000 * PAGE_SIZE;
 }
 
 /*
-- 
2.25.1