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memory-statistics.md

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Memory statistics

cat /proc/meminfo

MemTotal:       514916 kB
MemFree:        142676 kB
Buffers:         57068 kB
Cached:         214008 kB          # Page cache
SwapCached:          4 kB          # Cache of swap file
Active:         217180 kB          #  Active/inactive pages used by PFCA
Inactive:        99832 kB          #  
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:       514916 kB
LowFree:        142676 kB
SwapTotal:     1048568 kB
SwapFree:      1048552 kB
Dirty:               0 kB          # Cached file is modified and need to write to disk
Writeback:           0 kB          #  Being written to disk
AnonPages:       45932 kB
Mapped:          13576 kB
Slab:            47588 kB
PageTables:       1676 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:   1306024 kB
Committed_AS:   170724 kB
VmallocTotal:   507896 kB
VmallocUsed:      5440 kB
VmallocChunk:   502304 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     4096 kB

Cache

physical memory used to cache files usually result from calling mmap

fs/proc/proc_misc.c
...
cached = global_page_state(NR_FILE_PAGES) -
                   total_swapcache_pages - i.bufferram;
...

mm/filemap.c
...
int add_to_page_cache(struct page *page, struct address_space *mapping,
           pgoff_t offset, gfp_t gfp_mask)
{
...
                   __inc_zone_page_state(page, NR_FILE_PAGES);

SwapCached

When a page is swapped out, it goes through the same process as when writing a block of file to disk. So first go to cache and then the pdflush wil write it to block device. The benefit is possible merging many pages into single write (less IO operation).

Active/Inactive

Page Frame Reclaiming Algorithm maintains LRU lists of inactive and active page frames (physical memory page) that can be either assigned to processes or used as cache (excluding free pages).

fs/proc/proc_misc.c
...
get_zone_counts(&active, &inactive, &free);

Dirty

Amount of memory modified by processes and need to be written to files at some point of time. After calling sync, this should be zero

fs/proc/proc_misc.c
...
           K(global_page_state(NR_FILE_DIRTY)),

Writeback

Amount of memory being written to files. Should be zero, if the disk is fast enough.

fs/proc/proc_misc.c
...
          K(global_page_state(NR_WRITEBACK)),


fs/buffer.c
...
static int __block_write_full_page(struct inode *inode, struct page *page,
                   get_block_t *get_block, struct writeback_control *wbc)
...
   set_page_writeback(page);

References

  1. http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/4/html/Reference_Guie/s2-proc-meminfo.html
  2. fs/proc/proc_misc.c
  3. mm/filemap.c