Re: [PATCH 1/2] Protect larger order pages from breaking up

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[CC += linux-api@xxxxxxxxxxxxxxx]

Since this is a kernel-user-space API change, could you please CC
linux-api@ (and also for any future iterations of this patch series).
The kernel source file Documentation/SubmitChecklist notes that all
Linux kernel patches that change userspace interfaces should be CCed to
linux-api@xxxxxxxxxxxxxxx, so that the various parties who are
interested in API changes are informed. For further information, see
https://www.kernel.org/doc/man-pages/linux-api-ml.html

On 02/23/2018 04:03 AM, Christoph Lameter wrote:
> rfc->v1
>  - Use Thomas suggestion to change the test in __rmqueue_smallest
> 
> 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
> satify 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

Huh, that's rather weird interface to use. Writing to a general
statistics/info file for such specific functionality? Please no.

> or throught 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 32K 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.
> 
> So I redid his patch and this is the first draft of it.
> 
> 
> Idea-by: Thomas Schoebel-Theuer <tst@xxxxxxxxxxxxxxxxxx>
> 
> First performance tests in a virtual enviroment show
> a hackbench improvement by 6% just by increasing
> the page size used by the page allocator.

That's IMHO a rather weak justification for introducing a new userspace
API. What exactly has been set where? Could similar results be achieved
by tuning highatomic reservers and/or min_free_kbytes? I especially
wonder how much of the effects come from the associated watermarks
adjustment (which can be affected by min_free_kbytes) and what is due to
__rmqueue_smallest() changes. You changed the __rmqueue_smallest()
condition since RFC per Thomas suggestion, but report the same results?

> Signed-off-by: Christopher Lameter <cl@xxxxxxxxx>
> 
> 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
> @@ -1848,8 +1848,15 @@ 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
> +				       && current_order > order))

For watermarks we have various situations when we let a critical
allocation bypass them to some extent, but this is a strict condition.
That's potential for regressions.

Well, also not a fan of this patch, TBH. It's rather ad-hoc and not
backed up with results. Aside from the above points, I agree with the
objections of others for the RFC posting. It's also rather awkward that
watermarks are increased per the reservations, but when the reservations
are "consumed" (nr_free < min && current_order == order), the increased
watermarks are untouched. IMHO this further enlarges the effects of
purely adjusted watermarks by this patch.

Vlastimil

(leaving the rest of quoted mail for linux-api readers)

>  			continue;
> +
>  		list_del(&page->lru);
>  		rmv_page_order(page);
>  		area->nr_free--;
> @@ -5194,6 +5201,57 @@ static void build_zonelists(pg_data_t *p
>  
>  #endif	/* CONFIG_NUMA */
>  
> +int set_page_order_min(int node, int order, unsigned min)
> +{
> +	int i, o;
> +	long min_pages = 0;			/* Pages already reserved */
> +	long managed_pages = 0;			/* Pages managed on the node */
> +	struct zone *last = NULL;
> +	unsigned remaining;
> +
> +	/*
> +	 * Determine already reserved memory for orders
> +	 * plus the total of the pages on the node
> +	 */
> +	for (i = 0; i < MAX_NR_ZONES; i++) {
> +		struct zone *z = &NODE_DATA(node)->node_zones[i];
> +		if (managed_zone(z)) {
> +			for (o = 0; o < MAX_ORDER; o++) {
> +				if (o != order)
> +					min_pages += z->free_area[o].min << o;
> +
> +			}
> +			managed_pages += z->managed_pages;
> +		}
> +	}
> +
> +	if (min_pages + (min << order) > managed_pages / 2)
> +		return -ENOMEM;
> +
> +	/* Set the min values for all zones on the node */
> +	remaining = min;
> +	for (i = 0; i < MAX_NR_ZONES; i++) {
> +		struct zone *z = &NODE_DATA(node)->node_zones[i];
> +		if (managed_zone(z)) {
> +			u64 tmp;
> +
> +			tmp = (u64)z->managed_pages * (min << order);
> +			do_div(tmp, managed_pages);
> +			tmp >>= order;
> +			z->free_area[order].min = tmp;
> +
> +			last = z;
> +			remaining -= tmp;
> +		}
> +	}
> +
> +	/* Deal with rounding errors */
> +	if (remaining && last)
> +		last->free_area[order].min += remaining;
> +
> +	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
> @@ -5428,6 +5486,7 @@ 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;
>  	}
>  }
>  
> @@ -7002,6 +7061,7 @@ static void __setup_per_zone_wmarks(void
>  	unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);
>  	unsigned long lowmem_pages = 0;
>  	struct zone *zone;
> +	int order;
>  	unsigned long flags;
>  
>  	/* Calculate total number of !ZONE_HIGHMEM pages */
> @@ -7016,6 +7076,10 @@ static void __setup_per_zone_wmarks(void
>  		spin_lock_irqsave(&zone->lock, flags);
>  		tmp = (u64)pages_min * zone->managed_pages;
>  		do_div(tmp, lowmem_pages);
> +
> +		for (order = 0; order < MAX_ORDER; order++)
> +			tmp += zone->free_area[order].min << order;
> +
>  		if (is_highmem(zone)) {
>  			/*
>  			 * __GFP_HIGH and PF_MEMALLOC allocations usually don't
> 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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