[Devel] [PATCH vz9 05/16] x86: "pages zeroing on free" option introduced

[Nikita Yushchenko]

From: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>

This patch add pages zeroing option to free_pages_prepare().
It's disabled by default. To enable it one should add "zero-free-pages"
kernel option to kernel boot parameters.

Note, that kernel boot option handling and enabling of pages zeroing are
divided. The reason for this is that static keys initialization can't be
performed during kernel parameters parsing (can't specify, what is the exact
reason, but kernel just doesn't boot, if static key is incremented on
parameter callback). Because of this split, actual zeroing is enabled later
during kernel boot, but still early enough.

https://jira.sw.ru/browse/PSBM-33071

Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
Reviewed-by: Vladimir Davydov <vdavydov at virtuozzo.com>

+++
mm: Fix section mismatch of zero_free_pages

zero_free_pages is used not only from boot code:

WARNING: vmlinux.o(.text+0x21f668): Section mismatch in reference from the function __free_pages_ok() to the variable .init.data:zero_free_pages
The function __free_pages_ok() references
the variable __initdata zero_free_pages.
This is often because __free_pages_ok lacks a __initdata
annotation or the annotation of zero_free_pages is wrong.

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>

(cherry-picked from vz8 commit 26c485e52037 ("x86: "pages zeroing on free"
option introduced"))

Signed-off-by: Nikita Yushchenko <nikita.yushchenko at virtuozzo.com>
---
 mm/page_alloc.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 07512b81aa2e..aae89d58046f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -225,6 +225,24 @@ static inline void set_pcppage_migratetype(struct page *page, int migratetype)
 	page->index = migratetype;
 }
 
+static int zero_data_pages_enabled;
+struct static_key zero_free_pages = STATIC_KEY_INIT_FALSE;
+
+static int __init enable_zero_free_pages(char *__unused)
+{
+	zero_data_pages_enabled = 1;
+	return 1;
+}
+__setup("zero-free-pages", enable_zero_free_pages);
+
+static int __init setup_zero_free_pages(void)
+{
+	if (zero_data_pages_enabled)
+		static_key_slow_inc(&zero_free_pages);
+	return 0;
+}
+early_initcall(setup_zero_free_pages);
+
 #ifdef CONFIG_PM_SLEEP
 /*
  * The following functions are used by the suspend/hibernate code to temporarily
@@ -1330,6 +1348,9 @@ static __always_inline bool free_pages_prepare(struct page *page,
 				continue;
 			}
 			(page + i)->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+
+			if (static_key_false(&zero_free_pages))
+				clear_highpage(page + i);
 		}
 	}
 	if (PageMappingFlags(page))
@@ -1341,6 +1362,9 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	if (bad)
 		return false;
 
+	if (static_key_false(&zero_free_pages))
+		clear_highpage(page);
+
 	page_cpupid_reset_last(page);
 	page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
 	reset_page_owner(page, order);
-- 
2.30.2