Freeing Linux Virtual Memory
Hi,
I have Centos installed on HP Proliant Box with 13Gig of RAM Memory.
Yesterday, I was running rsync all my websites into another box in LAN.
Somehow the memory has dropped out and there is only 32Mb left on free memory.
Damn, only copying files has eating more than 12 Gigs of memory, and after rsync has finish and there is no more rsync process , the free mem won’t go back to normal. That is crazy !!.
I know you people will or even already have the same situation as I did.
Here is the tips. The secret is on /proc/sys/vm/drop_caches file.
Simply run this :
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
# echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
# echo 3 > /proc/sys/vm/drop_caches
Here is the example syntax and the result before and after freeing the memory.
[root@dev vm]# cd /proc/sys/vm/
[root@dev vm]# cat drop_caches
0
[root@dev vm]# free
total used free shared buffers cached
Mem: 1132664 1085076 47588 0 194664 490084
-/+ buffers/cache: 400328 732336
Swap: 2031608 0 2031608
[root@dev vm]# sync ; echo 3 > /proc/sys/vm/drop_caches ; free
total used free shared buffers cached
Mem: 1132664 388280 744384 0 116 48240
-/+ buffers/cache: 339924 792740
Swap: 2031608 0 2031608
You have new mail in /var/spool/mail/root
[root@dev vm]# cat drop_caches
3
[root@dev vm]# sync ; echo 0 > /proc/sys/vm/drop_caches ; free
total used free shared buffers cached
Mem: 1132664 395952 736712 0 1336 55180
-/+ buffers/cache: 339436 793228
Swap: 2031608 0 2031608
note: don’t forget to put ‘0′ back into the drop_caches.
I still dont know if there will the any risk, until now.. everything is fine.
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