On 6/25/21 3:53 PM, Michael S. Tsirkin wrote:

On Fri, Jun 25, 2021 at 09:47:08AM +0800, Gavin Shan wrote:

quoted

The macro PAGE_REPORTING_MIN_ORDER is defined as the page reporting
threshold. It can't be adjusted at runtime.

This introduces a variable (@page_reporting_order) to replace the
marcro (PAGE_REPORTING_MIN_ORDER). MAX_ORDER is assigned to it initially,
meaning the page reporting is disabled. It will be specified by driver
if valid one is provided. Otherwise, it will fall back to @pageblock_order.
It's also exported so that the page reporting order can be adjusted at
runtime.

Suggested-by: David Hildenbrand <redacted>
Signed-off-by: Gavin Shan <redacted>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
---
  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
  mm/page_reporting.c                             | 9 +++++++--
  mm/page_reporting.h                             | 5 ++---
  3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..566c4b9af3cd 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt

@@ -3566,6 +3566,12 @@
  			off: turn off poisoning (default)
  			on: turn on poisoning
  
+	page_reporting.page_reporting_order=
+			[KNL] Minimal page reporting order
+			Format: <integer>
+			Adjust the minimal page reporting order. The page
+			reporting is disabled when it exceeds (MAX_ORDER-1).

Which the admin knows how? Run grep in the kernel source?

Well, I guess it's fine as it's used for debugging purpose. I guess
it's mostly used by developers. Also, the value can be changed by
the module parameter in "/sys/module/page_reporting" either.

quoted

+
  	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
  			timeout > 0: seconds before rebooting
  			timeout = 0: wait forever

diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index df9c5054e1b4..34bf4d26c2c4 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c

@@ -4,12 +4,17 @@
  #include <linux/page_reporting.h>
  #include <linux/gfp.h>
  #include <linux/export.h>
+#include <linux/module.h>
  #include <linux/delay.h>
  #include <linux/scatterlist.h>
  
  #include "page_reporting.h"
  #include "internal.h"
  
+unsigned int page_reporting_order = MAX_ORDER;
+module_param(page_reporting_order, uint, 0644);
+MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");
+
  #define PAGE_REPORTING_DELAY	(2 * HZ)
  static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
  

@@ -229,7 +234,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
  
  	/* Generate minimum watermark to be able to guarantee progress */
  	watermark = low_wmark_pages(zone) +
-		    (PAGE_REPORTING_CAPACITY << PAGE_REPORTING_MIN_ORDER);
+		    (PAGE_REPORTING_CAPACITY << page_reporting_order);

Looks like this makes it easy to trigger undefined behaviour. Just use
any value > 31.

This function won't be run if page_reporting_order is more than (MAX_ORDER-1).

quoted

  
  	/*
  	 * Cancel request if insufficient free memory or if we failed

@@ -239,7 +244,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev,
  		return err;
  
  	/* Process each free list starting from lowest order/mt */
-	for (order = PAGE_REPORTING_MIN_ORDER; order < MAX_ORDER; order++) {
+	for (order = page_reporting_order; order < MAX_ORDER; order++) {
  		for (mt = 0; mt < MIGRATE_TYPES; mt++) {
  			/* We do not pull pages from the isolate free list */
  			if (is_migrate_isolate(mt))

diff --git a/mm/page_reporting.h b/mm/page_reporting.h
index 2c385dd4ddbd..c51dbc228b94 100644
--- a/mm/page_reporting.h
+++ b/mm/page_reporting.h

@@ -10,10 +10,9 @@
  #include <linux/pgtable.h>
  #include <linux/scatterlist.h>
  
-#define PAGE_REPORTING_MIN_ORDER	pageblock_order
-
  #ifdef CONFIG_PAGE_REPORTING
  DECLARE_STATIC_KEY_FALSE(page_reporting_enabled);
+extern unsigned int page_reporting_order;
  void __page_reporting_notify(void);
  
  static inline bool page_reported(struct page *page)

@@ -38,7 +37,7 @@ static inline void page_reporting_notify_free(unsigned int order)
  		return;
  
  	/* Determine if we have crossed reporting threshold */
-	if (order < PAGE_REPORTING_MIN_ORDER)
+	if (order < page_reporting_order)
  		return;
  
  	/* This will add a few cycles, but should be called infrequently */

-- 
2.23.0

Thanks,
Gavin