sudo sync && sudo sysctl -w vm.drop_caches=3 && sudo sysctl -w vm.drop_caches=0
The above line is a combination of three commands
1. sync --> to ensure any pending cache is flushed onto disk
2. sysctl -w vm.drop_caches = 3 --> to clear all caches (pagecache and inode/dentry caches)
3. sysctl -w vm.drop_caches = 0 --> reset the drop_caches to no clearing
The above command clears all caches from RAM. Beware, this clearing cache works in Ubuntu fine, but in other distributions maynot work fine
| Screenshot showing free RAM before clearing cache |
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| Screenshot showing free RAM after clearing cache |
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Thanx a lot.. it's very help full in my Squid Server.. before Squid Server using the memory, system take it for system's caching, and make Squid suffered, and restarting the system.. and i try to use your tips in cron hourly, hope this will help my problem.. Thanks again..
ReplyDeleteYou are welcome
ReplyDelete:)
This works very good. Thanks for the help!
ReplyDeleteYou are welcome. :)
ReplyDeletehow to create cron; to make this command running every 30 minutes?plz help me friend...:)
ReplyDeleteHi Helmi,
ReplyDeleteThese are the steps to create a crontab
1. Become root as sysctl will execute only with root privileges
sudo su
2. edit/create a new cron entry using the following command
crontab -e
3. paste the following line in the nano editor
*/30 * * * * sync && /sbin/sysctl -w vm.drop_caches=3 && /sbin/sysctl -w vm.drop_caches=0
4. save the file and exit and your cron will execute every 30 mins once and clear the cache
5. to list your root cron entries, use sudo crontab -l and to remove cron entries use sudo crontab -e
References
I followed the following two articles to get this cron working
http://adminschoice.com/crontab-quick-reference
http://www.willmaster.com/library/web-development/using_cron.php
why?
ReplyDeletewhy to clear cache memory?
ReplyDeleteIf you copy a big file (4 GB file) your RAM will be cached aggressively by linux. This may lead to RAM starvation though you have really loads of RAM, though it may be cleared by kernel after sometime.
Now you have two options, either to delete the copied file or unmount some filesystem where it is copied to free up RAM space.
Or you can forcefully clear the cache and reclaim it for some other applications use
why did I refer those pages for crontab?
ReplyDeleteBecause, I don't know them before and what do you think wrong in refering them ?
Or did you mean, why to use crontab ?
crontab is a scheduler through which you can schedule tasks to happen between scheduled intervals
This is a terrible idea. There is no benefit to dropping the cache AFTER anything good has already been wiped out. Cache is FIFO so dropping it now is essentially a no-op.
ReplyDeleteWhat you really want to do is stop the file copy from using the cache in the first place.
Try these:
http://enricozini.org/2010/tips/nocache/
https://code.google.com/p/pagecache-mangagement/
I still feel the necessity for clearing the cache, who asked linux to first cache my file when there is requirement for more RAM. Isn't it ridiculous to go so much as creating another program like nocache to avoid caching or write program yourself.
ReplyDeleteSee windows, it does not unnecessarily cache and even after large copy operations, it remains stable
And according to article it is saying it is based on swap. pagecache has nothing to do with swap, when pagecache overflows it is swapped which is very ugly
Caching a copy/move operation by OS is a bad idea, eventhough it caches, let us say if there is an upperlimit for caching it will be fine.
Why do you think people go for direct IO in databases, isn't it to avoid this stupid caching behavior
Hi Sankaran, I'm a very happy fan of your kernel compilation... howewer i have a question about this article:
ReplyDeletesudo sysctl -w vm.drop_caches=0 gives me an error (error: "Invalid argument" setting key "vm.drop_caches") while sudo sysctl -w vm.drop_caches=3 gives me not (1,2 value works fine too). Is there another way to reset the cache to no clearing instead of putting vm.drop_caches="0"? my kernel in your last 2.6.39 amd64 core2.
Keep up the good work!
Yeah, I checked it, vm.drop_caches=0 does not work
ReplyDeletewill update you, thanks for appreciation
know what, writing to drop_caches using
ReplyDeletesudo sysctl -w vm.drop_caches=3 immediately clears the pagecache, dentries and inodes
and clears again only if you call sysctl -w again, there is no need to explicitly set it back to 0, this is just my observation