[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: Hideo Aoki <haoki@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -155,6 +155,7 @@ extern void swapin_readahead(swp_entry_t, unsigned long, struct vm_area_struct *
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/* linux/mm/page_alloc.c */
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extern unsigned long totalram_pages;
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extern unsigned long totalhigh_pages;
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extern unsigned long totalreserve_pages;
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extern long nr_swap_pages;
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extern unsigned int nr_free_pages(void);
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extern unsigned int nr_free_pages_pgdat(pg_data_t *pgdat);
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@ -51,6 +51,7 @@ nodemask_t node_possible_map __read_mostly = NODE_MASK_ALL;
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EXPORT_SYMBOL(node_possible_map);
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unsigned long totalram_pages __read_mostly;
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unsigned long totalhigh_pages __read_mostly;
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unsigned long totalreserve_pages __read_mostly;
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long nr_swap_pages;
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int percpu_pagelist_fraction;
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@ -2476,6 +2477,38 @@ void __init page_alloc_init(void)
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hotcpu_notifier(page_alloc_cpu_notify, 0);
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}
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/*
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* calculate_totalreserve_pages - called when sysctl_lower_zone_reserve_ratio
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* or min_free_kbytes changes.
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*/
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static void calculate_totalreserve_pages(void)
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{
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struct pglist_data *pgdat;
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unsigned long reserve_pages = 0;
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int i, j;
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for_each_online_pgdat(pgdat) {
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for (i = 0; i < MAX_NR_ZONES; i++) {
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struct zone *zone = pgdat->node_zones + i;
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unsigned long max = 0;
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/* Find valid and maximum lowmem_reserve in the zone */
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for (j = i; j < MAX_NR_ZONES; j++) {
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if (zone->lowmem_reserve[j] > max)
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max = zone->lowmem_reserve[j];
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}
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/* we treat pages_high as reserved pages. */
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max += zone->pages_high;
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if (max > zone->present_pages)
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max = zone->present_pages;
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reserve_pages += max;
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}
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}
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totalreserve_pages = reserve_pages;
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}
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/*
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* setup_per_zone_lowmem_reserve - called whenever
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* sysctl_lower_zone_reserve_ratio changes. Ensures that each zone
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@ -2507,6 +2540,9 @@ static void setup_per_zone_lowmem_reserve(void)
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}
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}
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}
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/* update totalreserve_pages */
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calculate_totalreserve_pages();
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}
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/*
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@ -2561,6 +2597,9 @@ void setup_per_zone_pages_min(void)
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zone->pages_high = zone->pages_min + tmp / 2;
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spin_unlock_irqrestore(&zone->lru_lock, flags);
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}
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/* update totalreserve_pages */
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calculate_totalreserve_pages();
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}
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/*
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