Linux, using mmzone.h to gather information on memory mangagement stats

Question

I'm trying to create a system call that is able to report on memory management statistics. My goal is to be able to report on the following:

1. The Current number of free pages, over all memory zones.
2. The current number of pages used by slab allocator, over all memory zones.
3. The current number of pages in the active list, over all memory zones.
4. The current number of pages in the inactive list, over all memory zones.
5. The current number of pages in the active list whose reference bits are set, over all memory zones.
6. The current number of pages in the inactive list whose reference bits are set, over all memory zones.
7. The cumulative number of pages moved from the active list to the inactive list since the last machine boot.
8. Same as number seven but vice versa.

I'm not entirely knowledgeable on how to access this information. I know that in mmzone.h there is an array I can use called vm_stat injunction with the enum zone_stat_item and enum node_stat_item that will allow me to gather information about 1, but does mmzone.h contain information about 2 through 8. For example, would I use vm_stat[NR_SLAB_RECLAIMABLE] and vm_stat[NR_SLAB_UNRECLAIMABLE] to calculate 2? If not, where would I be able to access information that would satisfy 2 through 8? I'm confused because the variable names alone I find to be not very descriptive.

Answer 1

I don't know about 2,5,6,7, or 8. However, for 3 and 4 you can iterate through all the zones(using the for_each_zone macro that is also definedin mmzone.h ), and use the enum zone_stat_item:

    enum zone_stat_item {
    /* First 128 byte cacheline (assuming 64 bit words) */
    NR_FREE_PAGES,
    NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
    NR_ZONE_INACTIVE_ANON = NR_ZONE_LRU_BASE,
    NR_ZONE_ACTIVE_ANON,
    NR_ZONE_INACTIVE_FILE,
    NR_ZONE_ACTIVE_FILE,
    NR_ZONE_UNEVICTABLE,
    NR_ZONE_WRITE_PENDING,  /* Count of dirty, writeback and unstable pages */
    NR_MLOCK,       /* mlock()ed pages found and moved off LRU */
    NR_PAGETABLE,       /* used for pagetables */
    NR_KERNEL_STACK_KB, /* measured in KiB */
    /* Second 128 byte cacheline */
    NR_BOUNCE,
#if IS_ENABLED(CONFIG_ZSMALLOC)
    NR_ZSPAGES,     /* allocated in zsmalloc */
#endif
    NR_FREE_CMA_PAGES,
    NR_VM_ZONE_STAT_ITEMS };

If you take a look at vmstat.h you will find this useful function:

static inline unsigned long zone_page_state(struct zone *zone,
                enum zone_stat_item item){
long x = atomic_long_read(&zone->vm_stat[item]);
#ifdef CONFIG_SMP
if (x < 0)
    x = 0;
#endif
return x;

}

Which you can use to get the values for each of those elements in that enum. To get answer 3 you add the NR_ACTIVE_ANON with the NR_ACTIVE_FILE for each zone. For 4, you get the sum of NR_INACTIVE_ANON and NR_INACTIVE_FILE for each zone.

Let me know how you are able to get the remaining items if you end up figuring it out.