Re: Memory loss after long uptime

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On 04/27/2012 10:02 PM, Chris Adams wrote:
Once upon a time, Rick Stevens<ricks@xxxxxxxxxxxxxx>  said:
You might try having a look at the output of ipcs after stopping MySQL
and see if your missing memory is in one or more of the shm segments.
If so, you can reclaim it by using "ipcrm -m<shmid>". You'd be
surprised at how many programs don't release IPC resources--especially
if they are rudely terminated (e.g. SIGSEGV or SIGKILL).
Are you sure?  I've been running MySQL for a long time, and I don't
remember it ever using SysV IPC.  I certainly don't see it using that
now, even on an old version I still have running (much older than the
OP's F14).

To the OP: if you think you are seeing RAM in use that isn't reflected
when comparing the output of "free" to "ps"/"top" process usage, it
could be in other kernel buffers.  Check out "slabtop" (has to run as
root); there are other kernel caches that "free" doesn't know about,
especially the dentry and inode caches.  These will show up as just more
kernel RAM in use, but really they are caches that should be discarded
as needed (just like the old buffers/cache lines in "free").


Here's slabtop from one machine that's using too much RAM:

 Active / Total Objects (% used)    : 8516783 / 8967394 (95.0%)
 Active / Total Slabs (% used)      : 270701 / 270701 (100.0%)
 Active / Total Caches (% used)     : 68 / 101 (67.3%)
 Active / Total Size (% used)       : 5113995.32K / 5341810.93K (95.7%)
 Minimum / Average / Maximum Object : 0.01K / 0.59K / 8.00K

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME
3836868 3691157  96%    1.00K 119903       32   3836896K kmalloc-1024
3624368 3573469  98%    0.25K 113262       32    906096K kmalloc-256
570560 553390  96%    0.50K  17830       32    285280K kmalloc-512
197526 196494  99%    0.55K   3468       57    110976K radix_tree_node
140992 114638  81%    0.12K   4406       32     17624K kmalloc-128
113856  29876  26%    0.06K   1779       64      7116K kmalloc-64
 40448  40445  99%    0.01K     79      512       316K kmalloc-8
 35904  35485  98%    0.08K    704       51      2816K sysfs_dir_cache
 32724  26778  81%    1.69K   1818       18     58176K TCP
 29190  16929  57%    0.19K    695       42      5560K dentry
 26112  16386  62%    0.02K    102      256       408K ext4_io_page
...


Looks like the kmalloc-##s are taking up most of the space.
Question is, what (if anything) can be done about this on a running system? Any way to reclaim that memory?


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