Commit cb45b0e9 authored by Hideo AOKI's avatar Hideo AOKI Committed by Linus Torvalds
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[PATCH] overcommit: add calculate_totalreserve_pages() 



These patches are an enhancement of OVERCOMMIT_GUESS algorithm in
__vm_enough_memory().

- why the kernel needed patching

  When the kernel can't allocate anonymous pages in practice, currnet
  OVERCOMMIT_GUESS could return success. This implementation might be
  the cause of oom kill in memory pressure situation.

  If the Linux runs with page reservation features like
  /proc/sys/vm/lowmem_reserve_ratio and without swap region, I think
  the oom kill occurs easily.

- the overall design approach in the patch

  When the OVERCOMMET_GUESS algorithm calculates number of free pages,
  the reserved free pages are regarded as non-free pages.

  This change helps to avoid the pitfall that the number of free pages
  become less than the number which the kernel tries to keep free.

- testing results

  I tested the patches using my test kernel module.

  If the patches aren't applied to the kernel, __vm_enough_memory()
  returns success in the situation but autual page allocation is
  failed.

  On the other hand, if the patches are applied to the kernel, memory
  allocation failure is avoided since __vm_enough_memory() returns
  failure in the situation.

  I checked that on i386 SMP 16GB memory machine. I haven't tested on
  nommu environment currently.

This patch adds totalreserve_pages for __vm_enough_memory().

Calculate_totalreserve_pages() checks maximum lowmem_reserve pages and
pages_high in each zone. Finally, the function stores the sum of each
zone to totalreserve_pages.

The totalreserve_pages is calculated when the VM is initilized.
And the variable is updated when /proc/sys/vm/lowmem_reserve_raito
or /proc/sys/vm/min_free_kbytes are changed.

Signed-off-by: default avatarHideo Aoki <haoki@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e23ca00b

include/linux/swap.h

+1 −0
Original line number Diff line number Diff line
@@ -155,6 +155,7 @@ extern void swapin_readahead(swp_entry_t, unsigned long, struct vm_area_struct * 
/* linux/mm/page_alloc.c */

extern unsigned long totalram_pages;

extern unsigned long totalhigh_pages;

extern unsigned long totalreserve_pages;

extern long nr_swap_pages;

extern unsigned int nr_free_pages(void);

extern unsigned int nr_free_pages_pgdat(pg_data_t *pgdat);

mm/page_alloc.c

+39 −0
Original line number Diff line number Diff line
@@ -51,6 +51,7 @@ nodemask_t node_possible_map __read_mostly = NODE_MASK_ALL; 
EXPORT_SYMBOL(node_possible_map);

unsigned long totalram_pages __read_mostly;

unsigned long totalhigh_pages __read_mostly;

unsigned long totalreserve_pages __read_mostly;

long nr_swap_pages;

int percpu_pagelist_fraction;
@@ -2476,6 +2477,38 @@ void __init page_alloc_init(void) 
	hotcpu_notifier(page_alloc_cpu_notify, 0);

}



/*

 * calculate_totalreserve_pages - called when sysctl_lower_zone_reserve_ratio

 *	or min_free_kbytes changes.

 */

static void calculate_totalreserve_pages(void)

{

	struct pglist_data *pgdat;

	unsigned long reserve_pages = 0;

	int i, j;



	for_each_online_pgdat(pgdat) {

		for (i = 0; i < MAX_NR_ZONES; i++) {

			struct zone *zone = pgdat->node_zones + i;

			unsigned long max = 0;



			/* Find valid and maximum lowmem_reserve in the zone */

			for (j = i; j < MAX_NR_ZONES; j++) {

				if (zone->lowmem_reserve[j] > max)

					max = zone->lowmem_reserve[j];

			}



			/* we treat pages_high as reserved pages. */

			max += zone->pages_high;



			if (max > zone->present_pages)

				max = zone->present_pages;

			reserve_pages += max;

		}

	}

	totalreserve_pages = reserve_pages;

}



/*

 * setup_per_zone_lowmem_reserve - called whenever

 *	sysctl_lower_zone_reserve_ratio changes.  Ensures that each zone
@@ -2507,6 +2540,9 @@ static void setup_per_zone_lowmem_reserve(void) 
			}

		}

	}



	/* update totalreserve_pages */

	calculate_totalreserve_pages();

}



/*
@@ -2561,6 +2597,9 @@ void setup_per_zone_pages_min(void) 
		zone->pages_high  = zone->pages_min + tmp / 2;

		spin_unlock_irqrestore(&zone->lru_lock, flags);

	}



	/* update totalreserve_pages */

	calculate_totalreserve_pages();

}



/*