include/linux/low-mem-notify.h

   1 #ifndef _LINUX_LOW_MEM_NOTIFY_H
   2 #define _LINUX_LOW_MEM_NOTIFY_H
   3
   4 extern unsigned low_mem_margin_percent;
   5 extern unsigned long low_mem_minfree;
   6 void low_mem_notify(void);
   7 extern const struct file_operations low_mem_notify_fops;
   8
   9 /*
  10  * Return TRUE if we are in a low memory state.
  11  */
  12 static inline bool is_low_mem_situation(void)
  13 {
  14         const int lru_base = NR_LRU_BASE - LRU_BASE;
  15         const int file_mem_multiplier = 2;  /* between 1 and 2 seems right */
  16         /*
  17          * We declare a low-memory condition when free memory is low and there
  18          * isn't much reclaimable file memory.
  19          */
  20         unsigned long free_mem = global_page_state(NR_FREE_PAGES);
  21         unsigned long file_mem =
  22                         global_page_state(lru_base + LRU_ACTIVE_FILE) +
  23                         global_page_state(lru_base + LRU_INACTIVE_FILE);
  24         unsigned long min_file_mem = file_mem_multiplier *
  25                         (min_filelist_kbytes >> (PAGE_SHIFT - 10));
  26         bool is_low_mem = free_mem < low_mem_minfree && file_mem < min_file_mem;
  27
  28 #ifdef CONFIG_LOW_MEM_NOTIFY_DEBUG
  29         {
  30                 static bool was_low_mem;
  31                 if (is_low_mem && !was_low_mem)
  32                         printk(KERN_INFO "entering low_mem: %lu\n", in_use);
  33                 else if (!is_low_mem && was_low_mem)
  34                         printk(KERN_INFO "exiting low_mem: %lu\n", in_use);
  35                 was_low_mem = is_low_mem;
  36         }
  37 #endif
  38
  39         return is_low_mem;
  40 }
  41
  42 #endif