[Devel] [PATCH RHEL7 COMMIT] mm: add warning about high order allocations

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.11.6.vz7.42.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.11.6.vz7.42.1
------>
commit 2669ee7a8b5a8c5dd4c6a0ba02da63aa8da607a4
Author: Andrey Ryabinin <aryabinin at virtuozzo.com>
Date:   Thu Jan 18 16:35:05 2018 +0300

    mm: add warning about high order allocations
    
    Add sysctl vm.warn_high_order. If set it will warn about
    about allocations with order >= vm.warn_high_order.
    Prints only 32 warning at most and skips all __GFP_NOWARN allocations.
    Disabled by default.
    
    https://jira.sw.ru/browse/PSBM-79892
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 kernel/sysctl.c | 15 +++++++++++++++
 mm/page_alloc.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 9267ac19d76f..70f1219103a5 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -128,6 +128,7 @@ static int __maybe_unused one = 1;
 static int __maybe_unused two = 2;
 static int __maybe_unused four = 4;
 static unsigned long one_ul = 1;
+static int ten = 10;
 static int one_hundred = 100;
 #ifdef CONFIG_PRINTK
 static int ten_thousand = 10000;
@@ -174,6 +175,11 @@ extern int unaligned_dump_stack;
 extern int no_unaligned_warning;
 #endif
 
+extern int warn_order;
+extern int proc_warn_high_order(struct ctl_table *table, int write,
+			void __user *buffer, size_t *lenp, loff_t *ppos);
+
+
 static bool virtual_ptr(void **ptr, void *base, size_t size, void *cur);
 #define sysctl_virtual(sysctl)							\
 int sysctl ## _virtual(struct ctl_table *table, int write,			\
@@ -1657,6 +1663,15 @@ static struct ctl_table vm_table[] = {
 		.extra2		= &one_hundred,
 	},
 #endif
+	{
+		.procname	= "warn_high_order",
+		.data		= &warn_order,
+		.maxlen		= sizeof(warn_order),
+		.mode		= 0644,
+		.proc_handler	= &proc_warn_high_order,
+		.extra1		= &zero,
+		.extra2		= &ten,
+	},
 	{ }
 };
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 91e0681620b4..ec66148d09ba 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3136,6 +3136,37 @@ static void __alloc_collect_stats(gfp_t gfp_mask, unsigned int order,
 #endif
 }
 
+struct static_key warn_high_order_key = STATIC_KEY_INIT_FALSE;
+int warn_order = MAX_ORDER+1;
+
+int proc_warn_high_order(struct ctl_table *table, int write,
+			void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	int ret;
+
+	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	if (!ret) {
+		smp_wmb();
+		static_key_slow_inc(&warn_high_order_key);
+	}
+
+	return ret;
+}
+
+static __always_inline void warn_high_order(int order, gfp_t gfp_mask)
+{
+	static atomic_t warn_count = ATOMIC_INIT(32);
+
+	if (static_key_false(&warn_high_order_key)) {
+		int tmp_warn_order = smp_load_acquire(&warn_order);
+
+		if (order >= tmp_warn_order && !(gfp_mask & __GFP_NOWARN))
+			WARN(atomic_dec_return(&warn_count),
+				"order %d >= %d, gfp 0x%x\n",
+				order, tmp_warn_order, gfp_mask);
+	}
+}
+
 /*
  * This is the 'heart' of the zoned buddy allocator.
  */
@@ -3159,6 +3190,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	WARN_ON_ONCE((gfp_mask & __GFP_FS) && current->journal_info &&
 		!(current->flags & PF_MEMALLOC));
 
+	warn_high_order(order, gfp_mask);
+
 	if (should_fail_alloc_page(gfp_mask, order))
 		return NULL;