Script to clear swap and free memory...opinions

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Masterman
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PostPosted: Wed May 04, 2011 16:41    Post subject: Script to clear swap and free memory...opinions Reply with quote
After reading heavily on how kernel 2.6 manages memory, buffers and swaps, I stumbled upon this link where a user has implemented a simple bash script and has added it to his cronjobs:


http://ubuntuforums.org/showthread.php?t=1518922



In the OTRW thread, a user has posted a command that frees memory using the safe "sync" command:

Code:

sync; echo 3 > /proc/sys/vm/drop_caches; free


If this command is executed, the memory is freed, but the data on the swap partition is not, which could cause problems.

Here is the command before and after:

Code:
# free
             total         used         free       shared      buffers
Mem:        127036       115240        11796            0        47968
-/+ buffers:              67272        59764
Swap:       522072         4368       517704


Code:
# sync; echo 3 > /proc/sys/vm/drop_caches; free
             total         used         free       shared      buffers
Mem:        127036        18780       108256            0          216
-/+ buffers:              18564       108472
Swap:       522072         4360       517712


I am a heavy user of Samba and other memory intensive applications. Aside from a reboot, the used RAM always stays in the cache and is never freed.

Would running a cronjob like the example listed above, say every 12 hours (and at like 3 A.M) be a wise idea?

I can certainly understand that it could cause major issues if an application was running (say a user D/Ling from my FTP), so I am asking for your opinions.

Thanks,

Masterman
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oxygenx
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PostPosted: Thu May 05, 2011 8:32    Post subject: Re: Script to clear swap and free memory...opinions Reply with quote
Masterman wrote:

I am a heavy user of Samba and other memory intensive applications. Aside from a reboot, the used RAM always stays in the cache and is never freed.

Sure, because free memory is useless memory.
Quote:

Would running a cronjob like the example listed above, say every 12 hours (and at like 3 A.M) be a wise idea?

Probably not. If you have the feeling that your system uses to much ram for caches you can adjust the vm.vfs_cache_pressure sysctl, but looking at your # free "screenshot" that's not the case.
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Masterman
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PostPosted: Thu May 05, 2011 11:18    Post subject: Reply with quote
Thanks, I have read about the vfs_cache_pressure and have done the following:


Code:
root@Asus:~# echo 50 > /proc/sys/vm/vfs_cache_pressure
root@Asus:~# free
             total       used       free     shared    buffers     cached
Mem:        124708     117056       7652          0       1352      99492
-/+ buffers/cache:      16212     108496
Swap:      1052248          0    1052248


My free RAM is slowly being increased
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oxygenx
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PostPosted: Thu May 05, 2011 15:41    Post subject: Reply with quote
i doubt it will help you in any way, but if so i'd be glad to hear.
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ReDaLeRt
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PostPosted: Thu May 05, 2011 20:50    Post subject: Re: Script to clear swap and free memory...opinions Reply with quote
Masterman wrote:

http://ubuntuforums.org/showthread.php?t=1518922


WoW! Huge improvement on available memory.

I'll run this on the next weeks and give feedback.

Thanks m8!

[[]]
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drk2276
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Joined: 04 Jan 2019
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PostPosted: Mon Mar 23, 2020 12:18    Post subject: excellent script!!!! Reply with quote
although its a really old thread i would like to confirm that this script solved my problem with transmission!!
thank you!!!
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