[RFC] Protect larger order pages from breaking up

* [RFC] Protect larger order pages from breaking up
@ 2018-02-09 19:24 Christopher Lameter
  2018-02-12 17:36 ` Matthew Wilcox
  0 siblings, 1 reply; 4+ messages in thread
From: Christopher Lameter @ 2018-02-09 19:24 UTC (permalink / raw)
  To: Mel Gorman
  Cc: linux-mm, akpm, Leon Romanovsky, linux-rdma,
	Thomas Schoebel-Theuer, Matthew Wilcox

Over time as the kernel is churning through memory it will break
up larger pages and as time progresses larger contiguous allocations
will no longer be possible. This is an approach to preserve these
large pages and prevent them from being broken up.

This is useful for example for the use of jumbo pages and can
satisfy various needs of subsystems and device drivers that require
large contiguous allocation to operate properly.

The idea is to reserve a pool of pages of the required order
so that the kernel is not allowed to use the pages for allocations
of a different order. This is a pool that is fully integrated
into the page allocator and therefore transparently usable.

Control over this feature is by writing to /proc/zoneinfo.

F.e. to ensure that 2000 16K pages stay available for jumbo
frames do

	echo "3=2000" >/proc/zoneinfo

or through the order=<page spec> on the kernel command line.
F.e.

	order=3=2000,4N2=500

These pages will be subject to reclaim etc as usual but will not
be broken up.

One can then also f.e. operate the slub allocator with
64k pages. Specify "slub_max_order=3 slub_min_order=3" on
the kernel command line and all slab allocator allocations
will occur in 16K page sizes.

Note that this will reduce the memory available to the application
in some cases. Reclaim may occur more often. If more than
the reserved number of higher order pages are being used then
allocations will still fail as normal.

In order to make this work just right one needs to be able to
know the workload well enough to reserve the right amount
of pages. This is comparable to other reservation schemes.

Well that f.e brings up huge pages. You can of course
also use this to reserve those and can then be sure that
you can dynamically resize your huge page pools even after
a long time of system up time.

The idea for this patch came from Thomas Schoebel-Theuer whom I met
at the LCA and who described the approach to me promising
a patch that would do this. Sadly he has vanished somehow.
However, he has been using this approach to support a
production environment for numerous years. There was
a need for jumbo patches and large page support for
a couple of drivers it seems.

So I redid his patch and this is the first draft of it.

Idea-by: Thomas Schoebel-Theuer <tst@schoebel-theuer.de>

First performance tests in a virtual environment show
a hackbench improvement by 6% just by increasing
the page size used by the page allocator.

Signed-off-by: Christopher Lameter <cl@linux.com>

Index: linux/include/linux/mmzone.h
===================================================================

--- linux.orig/include/linux/mmzone.h
+++ linux/include/linux/mmzone.h
@@ -96,6 +96,11 @@ extern int page_group_by_mobility_disabl
 struct free_area {
 	struct list_head	free_list[MIGRATE_TYPES];
 	unsigned long		nr_free;
+	/* We stop breaking up pages of this order if less than
+	 * min are available. At that point the pages can only
+	 * be used for allocations of that particular order.
+	 */
+	unsigned long		min;
 };

 struct pglist_data;
Index: linux/mm/page_alloc.c
===================================================================
--- linux.orig/mm/page_alloc.c
+++ linux/mm/page_alloc.c
@@ -1844,7 +1844,12 @@ struct page *__rmqueue_smallest(struct z
 		area = &(zone->free_area[current_order]);
 		page = list_first_entry_or_null(&area->free_list[migratetype],
 							struct page, lru);
-		if (!page)
+		/*
+		 * Continue if no page is found or if our freelist contains
+		 * less than the minimum pages of that order. In that case
+		 * we better look for a different order.
+		 */
+		if (!page || area->nr_free < area->min)
 			continue;
 		list_del(&page->lru);
 		rmv_page_order(page);
@@ -5190,6 +5195,51 @@ static void build_zonelists(pg_data_t *p

 #endif	/* CONFIG_NUMA */

+int set_page_order_min(int node, int order, unsigned min)
+{
+	struct free_area *a;
+	long m;
+	enum zone_type zone_type = MAX_NR_ZONES;
+	int i;
+	int managed_pages = 0;
+	struct zone *zone;
+
+	/* Find the largest zone on the node */
+	for (i = 0; i < MAX_NR_ZONES; i++) {
+		struct zone *z = &NODE_DATA(node)->node_zones[i];
+		if (managed_zone(z)) {
+			if (z->managed_pages > managed_pages) {
+				managed_pages = z->managed_pages;
+				zone_type = i;
+				zone = z;
+				a = &z->free_area[order];
+			}
+		}
+	}
+
+	BUG_ON(zone_type == MAX_NR_ZONES);
+	m = min - a->min;
+
+	/* Maximum allowed is half of memory */
+	if (m > 0 && (m << order) > managed_pages / 2)
+		return -ENOMEM;
+
+	/*
+	 * Update watermarks
+	 *
+	 * Note that this is for the worst case where all pages of the order
+	 * have to be kept unallocated. In a properly configured system these
+	 * pages will be used. Maybe this could be done differently to avoid
+	 * too frequent reclaim?
+	 */
+	printk(KERN_INFO "Protecting %d pages of order %d from breakup\n", min, order);
+	spin_lock(&managed_page_count_lock);
+	zone->managed_pages -= m << order;
+	a->min = min;
+	spin_unlock(&managed_page_count_lock);
+	return 0;
+}
+
 /*
  * Boot pageset table. One per cpu which is going to be used for all
  * zones and all nodes. The parameters will be set in such a way
@@ -5424,6 +5474,7 @@ static void __meminit zone_init_free_lis
 	for_each_migratetype_order(order, t) {
 		INIT_LIST_HEAD(&zone->free_area[order].free_list[t]);
 		zone->free_area[order].nr_free = 0;
+		zone->free_area[order].min = 0;
 	}
 }

Index: linux/mm/vmstat.c
===================================================================
--- linux.orig/mm/vmstat.c
+++ linux/mm/vmstat.c
@@ -27,6 +27,7 @@
 #include <linux/mm_inline.h>
 #include <linux/page_ext.h>
 #include <linux/page_owner.h>
+#include <linux/ctype.h>

 #include "internal.h"

@@ -1614,6 +1615,11 @@ static void zoneinfo_show_print(struct s
 				zone_numa_state_snapshot(zone, i));
 #endif

+	for (i = 0; i < MAX_ORDER; i++)
+		if (zone->free_area[i].min)
+			seq_printf(m, "\nPreserve %lu pages of order %d from breaking up.",
+				zone->free_area[i].min, i);
+
 	seq_printf(m, "\n  pagesets");
 	for_each_online_cpu(i) {
 		struct per_cpu_pageset *pageset;
@@ -1641,6 +1647,122 @@ static void zoneinfo_show_print(struct s
 	seq_putc(m, '\n');
 }

+static int __order_protect(char *p)
+{
+	char c;
+
+	do {
+		int order = 0;
+		int pages = 0;
+		int node = 0;
+		int rc;
+
+		/* Syntax <order>[N<node>]=number */
+		if (!isdigit(*p))
+			return -EFAULT;
+
+		while (true) {
+			c = *p++;
+
+			if (!isdigit(c))
+				break;
+
+			order = order * 10 + c - '0';
+		}
+
+		/* Check for optional node specification */
+		if (c == 'N') {
+			if (!isdigit(*p))
+				return -EFAULT;
+
+			while (true) {
+				c = *p++;
+				if (!isdigit(c))
+					break;
+				node = node * 10 + c - '0';
+			}
+		}
+
+		if (c != '=')
+			return -EINVAL;
+
+		if (!isdigit(*p))
+			return -EINVAL;
+
+		while (true) {
+			c = *p++;
+			if (!isdigit(c))
+				break;
+			pages = pages * 10 + c - '0';
+		}
+
+		if (order == 0 || order >= MAX_ORDER)
+		       return -EINVAL;
+
+		if (!node_online(node))
+			return -ENOSYS;
+
+		rc = set_page_order_min(node, order, pages);
+		if (rc)
+			return rc;
+
+	} while (c == ',');
+
+	if (c)
+		return -EINVAL;
+
+	setup_per_zone_wmarks();
+
+	return 0;
+}
+
+/*
+ * Writing to /proc/zoneinfo allows to setup the large page breakup
+ * protection.
+ *
+ * Syntax:
+ * 	<order>[N<node>]=<number>{,<order>[N<node>]=<number>}
+ *
+ * F.e. Protecting 500 pages of order 2 (16K on intel) and 300 of
+ * order 4 (64K) on node 1
+ *
+ * 	echo "2=500,4N1=300" >/proc/zoneinfo
+ *
+ */
+static ssize_t zoneinfo_write(struct file *file, const char __user *buffer,
+			size_t count, loff_t *ppos)
+{
+	char zinfo[200];
+	int rc;
+
+	if (count > sizeof(zinfo))
+		return -EINVAL;
+
+	if (copy_from_user(zinfo, buffer, count))
+		return -EFAULT;
+
+	zinfo[count - 1] = 0;
+
+	rc = __order_protect(zinfo);
+
+	if (rc)
+		return rc;
+
+	return count;
+}
+
+static int order_protect(char *s)
+{
+	int rc;
+
+	rc = __order_protect(s);
+	if (rc)
+		printk("Invalid order=%s rc=%d\n",s, rc);
+
+	return 1;
+}
+__setup("order=", order_protect);
+
 /*
  * Output information about zones in @pgdat.  All zones are printed regardless
  * of whether they are populated or not: lowmem_reserve_ratio operates on the
@@ -1672,6 +1794,7 @@ static const struct file_operations zone
 	.read		= seq_read,
 	.llseek		= seq_lseek,
 	.release	= seq_release,
+	.write		= zoneinfo_write,
 };

 enum writeback_stat_item {
@@ -2016,7 +2139,7 @@ void __init init_mm_internals(void)
 	proc_create("buddyinfo", 0444, NULL, &buddyinfo_file_operations);
 	proc_create("pagetypeinfo", 0444, NULL, &pagetypeinfo_file_operations);
 	proc_create("vmstat", 0444, NULL, &vmstat_file_operations);
-	proc_create("zoneinfo", 0444, NULL, &zoneinfo_file_operations);
+	proc_create("zoneinfo", 0644, NULL, &zoneinfo_file_operations);
 #endif
 }

Index: linux/include/linux/gfp.h
===================================================================
--- linux.orig/include/linux/gfp.h
+++ linux/include/linux/gfp.h
@@ -543,6 +543,7 @@ void drain_all_pages(struct zone *zone);
 void drain_local_pages(struct zone *zone);

 void page_alloc_init_late(void);
+int set_page_order_min(int node, int order, unsigned min);

 /*
  * gfp_allowed_mask is set to GFP_BOOT_MASK during early boot to restrict what

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