[RFC PATCH 01/16] mm: Page Alloc Hogger module

[Juan Yescas <jyescas@google.com>]

This patch contains the skeleton for the Pagei Alloc Hogger. It creates the
"mm" dir that will be the base directory that will contain the "free" file
and the "node-<x>" dirs.

Signed-off-by: Juan Yescas <jyescas@google.com>
---
 mm/Kconfig.debug       |  12 +++++
 mm/Makefile            |   1 +
 mm/page_alloc_hogger.c | 115 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 128 insertions(+)
 create mode 100644 mm/page_alloc_hogger.c

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 7638d75b27db..c8fcecdca6ac 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -309,3 +309,15 @@ config PER_VMA_LOCK_STATS
 	  overhead in the page fault path.
 
 	  If in doubt, say N.
+
+config PAGEALLOC_HOGGER
+	bool "Alloc pages from different nodes, zones, migrate types and orders"
+	depends on DEBUG_FS
+	help
+	  Say Y to alloc pages from different nodes, zones, migrate type and
+	  orders using the debug fs filesystem. This helps to generate memory
+	  pressure easily. This is useful to debug memory reclaims issues,
+	  OOM triggers, page migration issues, etc.
+
+	  If in doubt, say N.
+
diff --git a/mm/Makefile b/mm/Makefile
index 2d0570a16e5b..b48f2ac6ee80 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -133,6 +133,7 @@ obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
 obj-$(CONFIG_DEBUG_PAGEALLOC) += debug_page_alloc.o
 obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o
 obj-$(CONFIG_DAMON) += damon/
+obj-$(CONFIG_PAGEALLOC_HOGGER) += page_alloc_hogger.o
 obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o
 obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o
 obj-$(CONFIG_ZONE_DEVICE) += memremap.o
diff --git a/mm/page_alloc_hogger.c b/mm/page_alloc_hogger.c
new file mode 100644
index 000000000000..dfdc2ee2eafe
--- /dev/null
+++ b/mm/page_alloc_hogger.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Page allocator DebugFS Interface
+ * Author: Juan Yescas <jyescas@google.com>
+ *
+ * This module allows to make page allocs per node, zone, migrate type
+ * and order using the DebugFS filesystem.
+ *
+ * When this module is installed and the debugfs is mounted, the "mm" directory
+ " will be created in <debugfs mount point>/mm" directory. Under this directory,
+ * there will be subdirs to select the nodes, zones, orders and migrate type.
+ *
+ * For example:
+ *
+ *      /sys/kernel/debug/mm/
+ *      |-- free
+ *      `-- node-0
+ *         |-- zone-DMA
+ *         |   |-- order-0
+ *         |   |   |-- migrate-HighAtomic
+ *         |   |   |   `-- nr_pages_allocs
+ *         |   |   |-- migrate-Movable
+ *         |   |   |   `-- nr_pages_allocs
+ *         |   |   |-- migrate-Reclaimable
+ *         |   |   |   `-- nr_pages_allocs
+ *         |   |   `-- migrate-Unmovable
+ *         |   |       `-- nr_pages_allocs
+ *         |   |-- ...
+ *         |   |
+ *         |   `-- order-9
+ *         |       |-- migrate-HighAtomic
+ *         |       |   `-- nr_pages_allocs
+ *         |       |-- migrate-Movable
+ *         |       |   `-- nr_pages_allocs
+ *         |       |-- migrate-Reclaimable
+ *         |       |   `-- nr_pages_allocs
+ *         |       `-- migrate-Unmovable
+ *         |           `-- nr_pages_allocs
+ *         `-- zone-Normal
+ *             |-- order-0
+ *             |   |-- migrate-HighAtomic
+ *             |   |   `-- nr_pages_allocs
+ *             |   |-- migrate-Movable
+ *             |   |   `-- nr_pages_allocs
+ *             |   |-- migrate-Reclaimable
+ *             |   |   `-- nr_pages_allocs
+ *             |   `-- migrate-Unmovable
+ *             |       `-- nr_pages_allocs
+ *             |-- ....
+ *             |
+ *             `-- order-9
+ *                 |-- migrate-HighAtomic
+ *                 |   `-- nr_pages_allocs
+ *                 |-- migrate-Movable
+ *                 |   `-- nr_pages_allocs
+ *                 |-- migrate-Reclaimable
+ *                 |   `-- nr_pages_allocs
+ *                 `-- migrate-Unmovable
+ *                     `-- nr_pages_allocs
+ *
+ * Usage:
+ *
+ * 1. To trigger the allocation, navigate to the debugfs path corresponding
+ *    to your target node, memory zone, allocation order, and migration type,
+ *    then write the requested allocation count to nr_pages_allocs.
+ *
+ *    For example, to make 3 allocs of order 9, Migrate Type Movable,
+ *    Zone Normal and Node 0, run:
+ *
+ *    $ echo 3 > /sys/kernel/debug/mm/node-0/zone-Normal/order-9/migrate-Movable/nr_pages_allocs
+ *
+ * 2. For each allocation created, a corresponding file named sequentially
+ *    (1, 2, n) will appear in that directory.
+ *
+ *    $ ls /sys/kernel/debug/mm/node-0/zone-Normal/order-9/migrate-Movable/
+ *    1   2   3  nr_pages_allocs
+ *
+ * 3. To free the allocation, write the allocation file name in /sys/kernel/debug/mm/free.
+ *    For example, to release the 2nd allocation run:
+ *
+ *    $ echo 2 > /sys/kernel/debug/mm/free
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/errno.h>
+#include <linux/debugfs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+struct dentry *mmdir;
+
+static int __init page_alloc_hogger_debugfs_init(void)
+{
+	mmdir = debugfs_create_dir("mm", NULL);
+	if (IS_ERR(mmdir)) {
+		pr_err("Unable to create mm directory");
+		return PTR_ERR(mmdir);
+	}
+
+	return 0;
+}
+
+static void __exit page_alloc_hogger_debugfs_exit(void)
+{
+	debugfs_remove_recursive(mmdir);
+}
+
+module_init(page_alloc_hogger_debugfs_init);
+module_exit(page_alloc_hogger_debugfs_exit);
+
+MODULE_AUTHOR("Juan Yescas");
+MODULE_DESCRIPTION("Module to alloc pages to generate memory pressure");
+MODULE_LICENSE("GPL");
-- 
2.55.0.229.g6434b31f56-goog