[PATCH v2 0/2] clarify limitations of hibernation

[PATCH v2 0/2] clarify limitations of hibernation

[Luigi Semenzato]

These patches aim to make it clearer under which circumstances
hibernation will function as expected.  They include one documentation
change, and one change which logs more information on failure to
enter hibernation.

Luigi Semenzato (2):
  Documentation: clarify limitations of hibernation
  pm: add more logging on hibernation failure

 Documentation/admin-guide/pm/sleep-states.rst | 12 +++++++++++-
 kernel/power/snapshot.c                       | 18 ++++++++++++------
 2 files changed, 23 insertions(+), 7 deletions(-)

-- 
2.24.1.735.g03f4e72817-goog

[PATCH v2 1/2] Documentation: clarify limitations of hibernation

[Luigi Semenzato]

Entering hibernation (suspend-to-disk) will fail if the kernel
cannot allocate enough memory to create a snapshot of all pages
in use; i.e., if memory in use is over 1/2 of total RAM.  This
patch makes this limitation clearer in the documentation.  Without
it, users may assume that hibernation can replace suspend-to-RAM
when in fact its functionality is more limited.

Signed-off-by: Luigi Semenzato <semenzato@google.com>
---
 Documentation/admin-guide/pm/sleep-states.rst | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/pm/sleep-states.rst b/Documentation/admin-guide/pm/sleep-states.rst
index cd3a28cb81f4..a2d5632b7856 100644
--- a/Documentation/admin-guide/pm/sleep-states.rst
+++ b/Documentation/admin-guide/pm/sleep-states.rst
@@ -112,7 +112,9 @@ Hibernation
 This state (also referred to as Suspend-to-Disk or STD) offers the greatest
 energy savings and can be used even in the absence of low-level platform support
 for system suspend.  However, it requires some low-level code for resuming the
-system to be present for the underlying CPU architecture.
+system to be present for the underlying CPU architecture.  Additionally, the
+current implementation can enter the hibernation state only when memory
+usage is sufficiently low (see "Limitations" below).
 
 Hibernation is significantly different from any of the system suspend variants.
 It takes three system state changes to put it into hibernation and two system
@@ -149,6 +151,14 @@ Hibernation is supported if the :c:macro:`CONFIG_HIBERNATION` kernel
 configuration option is set.  However, this option can only be set if support
 for the given CPU architecture includes the low-level code for system resume.
 
+Limitations of Hibernation
+==========================
+
+When entering hibernation, the kernel tries to allocate a chunk of memory large
+enough to contain a copy of all pages in use, to use it for the system
+snapshot.  If the allocation fails, the system cannot hibernate and the
+operation fails with ENOMEM.  This will happen, for instance, when the total
+amount of anonymous pages (process data) exceeds 1/2 of total RAM.
 
 Basic ``sysfs`` Interfaces for System Suspend and Hibernation
 =============================================================
-- 
2.24.1.735.g03f4e72817-goog

[PATCH v2 2/2] pm: add more logging on hibernation failure

[Luigi Semenzato]

Hibernation fails when the kernel cannot allocate enough memory
to copy all pages in use.  This patch ensures that the failure
reason is clearly logged.

Signed-off-by: Luigi Semenzato <semenzato@google.com>
---
 kernel/power/snapshot.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 26b9168321e7..df498717a97e 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1705,16 +1705,20 @@ int hibernate_preallocate_memory(void)
 	ktime_t start, stop;
 	int error;
 
-	pr_info("Preallocating image memory... ");
+	pr_info("Preallocating hibernation image memory\n");
 	start = ktime_get();
 
 	error = memory_bm_create(&orig_bm, GFP_IMAGE, PG_ANY);
-	if (error)
+	if (error) {
+		pr_err("Cannot allocate original bitmap\n");
 		goto err_out;
+	}
 
 	error = memory_bm_create(&copy_bm, GFP_IMAGE, PG_ANY);
-	if (error)
+	if (error) {
+		pr_err("Cannot allocate copy bitmap\n");
 		goto err_out;
+	}
 
 	alloc_normal = 0;
 	alloc_highmem = 0;
@@ -1804,8 +1808,11 @@ int hibernate_preallocate_memory(void)
 		alloc -= pages;
 		pages += pages_highmem;
 		pages_highmem = preallocate_image_highmem(alloc);
-		if (pages_highmem < alloc)
+		if (pages_highmem < alloc) {
+			pr_err("Image allocation is %lu pages short\n",
+				alloc - pages_highmem);
 			goto err_out;
+		}
 		pages += pages_highmem;
 		/*
 		 * size is the desired number of saveable pages to leave in
@@ -1836,13 +1843,12 @@ int hibernate_preallocate_memory(void)
 
  out:
 	stop = ktime_get();
-	pr_cont("done (allocated %lu pages)\n", pages);
+	pr_info("Allocated %lu pages for hibernation shapshot\n", pages);
 	swsusp_show_speed(start, stop, pages, "Allocated");
 
 	return 0;
 
  err_out:
-	pr_cont("\n");
 	swsusp_free();
 	return -ENOMEM;
 }
-- 
2.24.1.735.g03f4e72817-goog

RE: [PATCH v2 2/2] pm: add more logging on hibernation failure

[Elliott, Robert (Servers)]

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org <linux-kernel-
> owner@vger.kernel.org> On Behalf Of Luigi Semenzato
> Sent: Thursday, January 2, 2020 2:01 PM
> To: linux-pm@vger.kernel.org
...
> -	pr_info("Preallocating image memory... ");
> +	pr_info("Preallocating hibernation image memory\n");
...
> +		pr_err("Cannot allocate original bitmap\n");
...
> +		pr_err("Cannot allocate copy bitmap\n");
...
> +			pr_err("Image allocation is %lu pages short\n",
> +				alloc - pages_highmem);
...
> -	pr_cont("done (allocated %lu pages)\n", pages);
> +	pr_info("Allocated %lu pages for hibernation shapshot\n", pages);
>  	swsusp_show_speed(start, stop, pages, "Allocated");

Including the word "hibernation" or the phrase "hibernation image" in
each print would help in parsing the messages (e.g., with grep).