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Commit 12462755 authored by Rik van Riel's avatar Rik van Riel Committed by Vinayak Menon
Browse files

add extra free kbytes tunable 



Add a userspace visible knob to tell the VM to keep an extra amount
of memory free, by increasing the gap between each zone's min and
low watermarks.

This is useful for realtime applications that call system
calls and have a bound on the number of allocations that happen
in any short time period.  In this application, extra_free_kbytes
would be left at an amount equal to or larger than than the
maximum number of allocations that happen in any burst.

It may also be useful to reduce the memory use of virtual
machines (temporarily?), in a way that does not cause memory
fragmentation like ballooning does.

[ccross]
Revived for use on old kernels where no other solution exists.
The tunable will be removed on kernels that do better at avoiding
direct reclaim.

Change-Id: I765a42be8e964bfd3e2886d1ca85a29d60c3bb3e
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarColin Cross <ccross@android.com>
Git-commit: f8ade3666c8612c33929f499b3c8800d83f43d84
Git-repo: https://android.googlesource.com/kernel/common.git


[vinmenon@codeaurora.org: avoid user setting of watermark_scale_factor
to any value other than 0, make the default watermark_scale_factor 0,
changes because of the presence of watermark_scale_factor. Move the
declaration of extra_free_kbytes to include file and remove the
initialization to zero in the definition. This fixes the checkpatch
warnings. Make the inclusion of variable "one_thousand" in kernel/sysctl.c
dependent on CONFIG_PERF_EVENTS which is the only user left now (earlier
being watermark_scale_factor]
Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
parent d0edcda0

Documentation/sysctl/vm.txt

+16 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ Currently, these files are in /proc/sys/vm: 
- dirty_writeback_centisecs

- drop_caches

- extfrag_threshold

- extra_free_kbytes

- hugepages_treat_as_movable

- hugetlb_shm_group

- laptop_mode
@@ -240,6 +241,21 @@ fragmentation index is <= extfrag_threshold. The default value is 500. 


==============================================================



extra_free_kbytes



This parameter tells the VM to keep extra free memory between the threshold

where background reclaim (kswapd) kicks in, and the threshold where direct

reclaim (by allocating processes) kicks in.



This is useful for workloads that require low latency memory allocations

and have a bounded burstiness in memory allocations, for example a

realtime application that receives and transmits network traffic

(causing in-kernel memory allocations) with a maximum total message burst

size of 200MB may need 200MB of extra free memory to avoid direct reclaim

related latencies.



==============================================================



hugepages_treat_as_movable



This parameter controls whether we can allocate hugepages from ZONE_MOVABLE

include/linux/mm.h

+1 −0
Original line number Diff line number Diff line
@@ -1901,6 +1901,7 @@ extern void zone_pcp_reset(struct zone *zone); 
/* page_alloc.c */

extern int min_free_kbytes;

extern int watermark_scale_factor;

extern int extra_free_kbytes;



/* nommu.c */

extern atomic_long_t mmap_pages_allocated;

kernel/sysctl.c

+12 −2
Original line number Diff line number Diff line
@@ -127,7 +127,9 @@ static int __maybe_unused three = 3; 
static int __maybe_unused four = 4;

static unsigned long one_ul = 1;

static int one_hundred = 100;

#ifdef CONFIG_PERF_EVENTS

static int one_thousand = 1000;

#endif

#ifdef CONFIG_PRINTK

static int ten_thousand = 10000;

#endif
@@ -1572,8 +1574,16 @@ static struct ctl_table vm_table[] = { 
		.maxlen		= sizeof(watermark_scale_factor),

		.mode		= 0644,

		.proc_handler	= watermark_scale_factor_sysctl_handler,

		.extra1		= &one,

		.extra2		= &one_thousand,

		.extra1		= &zero,

		.extra2		= &zero,

	},

	{

		.procname	= "extra_free_kbytes",

		.data		= &extra_free_kbytes,

		.maxlen		= sizeof(extra_free_kbytes),

		.mode		= 0644,

		.proc_handler	= min_free_kbytes_sysctl_handler,

		.extra1		= &zero,

	},

	{

		.procname	= "percpu_pagelist_fraction",

mm/page_alloc.c

+26 −9
Original line number Diff line number Diff line
@@ -254,9 +254,21 @@ compound_page_dtor * const compound_page_dtors[] = { 
#endif

};



/*

 * Try to keep at least this much lowmem free.  Do not allow normal

 * allocations below this point, only high priority ones. Automatically

 * tuned according to the amount of memory in the system.

 */

int min_free_kbytes = 1024;

int user_min_free_kbytes = -1;

int watermark_scale_factor = 10;

int watermark_scale_factor;



/*

 * Extra memory for the system to try freeing. Used to temporarily

 * free memory, to make space for new workloads. Anyone can allocate

 * down to the min watermarks controlled by min_free_kbytes above.

 */

int extra_free_kbytes;



static unsigned long __meminitdata nr_kernel_pages;

static unsigned long __meminitdata nr_all_pages;
@@ -6742,6 +6754,7 @@ static void setup_per_zone_lowmem_reserve(void) 
static void __setup_per_zone_wmarks(void)

{

	unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);

	unsigned long pages_low = extra_free_kbytes >> (PAGE_SHIFT - 10);

	unsigned long lowmem_pages = 0;

	struct zone *zone;

	unsigned long flags;
@@ -6753,11 +6766,14 @@ static void __setup_per_zone_wmarks(void) 
	}



	for_each_zone(zone) {

		u64 tmp;

		u64 min, low;



		spin_lock_irqsave(&zone->lock, flags);

		tmp = (u64)pages_min * zone->managed_pages;

		do_div(tmp, lowmem_pages);

		min = (u64)pages_min * zone->managed_pages;

		do_div(min, lowmem_pages);

		low = (u64)pages_low * zone->managed_pages;

		do_div(low, vm_total_pages);



		if (is_highmem(zone)) {

			/*

			 * __GFP_HIGH and PF_MEMALLOC allocations usually don't
@@ -6778,7 +6794,7 @@ static void __setup_per_zone_wmarks(void) 
			 * If it's a lowmem zone, reserve a number of pages

			 * proportionate to the zone's size.

			 */

			zone->watermark[WMARK_MIN] = tmp;

			zone->watermark[WMARK_MIN] = min;

		}



		/*
@@ -6786,12 +6802,13 @@ static void __setup_per_zone_wmarks(void) 
		 * scale factor in proportion to available memory, but

		 * ensure a minimum size on small systems.

		 */

		tmp = max_t(u64, tmp >> 2,

		min = max_t(u64, min >> 2,

			    mult_frac(zone->managed_pages,

				      watermark_scale_factor, 10000));



		zone->watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;

		zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;

		zone->watermark[WMARK_LOW]  = min_wmark_pages(zone) + low + min;

		zone->watermark[WMARK_HIGH] =

					min_wmark_pages(zone) + low + min * 2;



		spin_unlock_irqrestore(&zone->lock, flags);

	}
@@ -6872,7 +6889,7 @@ core_initcall(init_per_zone_wmark_min) 
/*

 * min_free_kbytes_sysctl_handler - just a wrapper around proc_dointvec() so

 *	that we can call two helper functions whenever min_free_kbytes

 *	changes.

 *	or extra_free_kbytes changes.

 */

int min_free_kbytes_sysctl_handler(struct ctl_table *table, int write,

	void __user *buffer, size_t *length, loff_t *ppos)