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I read about Linux and cachd memory at linuxatemyram but there is something that doesn't make sense to me, if the server have even a low load, instead of freeing some cached memory it starts using swap, which makes the server slow..

Even now, when the server load is load average: 0.00, 0.00, 0.00 some memory is swapped while over 85% of the memory is taken for swapping.

I read similar questions such as this and this, but it's mentioned that swapping shouldn't happen. As well, up until 3 weeks ago a much smaller part of the memory was taken by cache, and we didn't change anything that was suppose to affect the cached memory.

Could you please tell me if this values are still OK or could it be that i have a problem?

Thanks!

[root@web01 ~]# cat /proc/meminfo MemTotal: 5183448 kB MemFree: 249260 kB Buffers: 330848 kB Cached: 4317828 kB SwapCached: 92 kB Active: 2883596 kB Inactive: 1882468 kB HighTotal: 4315324 kB HighFree: 63516 kB LowTotal: 868124 kB LowFree: 185744 kB SwapTotal: 5799928 kB SwapFree: 5799796 kB Dirty: 368 kB Writeback: 0 kB AnonPages: 117356 kB Mapped: 21076 kB Slab: 152668 kB PageTables: 4184 kB NFS_Unstable: 0 kB Bounce: 0 kB CommitLimit: 8391652 kB Committed_AS: 268708 kB VmallocTotal: 116728 kB VmallocUsed: 5404 kB VmallocChunk: 110964 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 Hugepagesize: 2048 kB 

[root@web01 ~]# free total used free shared buffers cached Mem: 5183448 4932936 250512 0 330840 4317340 -/+ buffers/cache: 284756 4898692 Swap: 5799928 132 5799796 

[root@web01 ~]# uname -a Linux web01 2.6.18-164.15.1.el5PAE #1 SMP Wed Mar 17 12:14:29 EDT 2010 i686 i686 i386 GNU/Linux
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    The idea that swap makes a system slow is entirely false. Your system will use swap only when it is beneficial to do so. Commented May 26, 2014 at 2:59

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No! In your example post, effectively nothing is used for swap. You're using 92k (or 132k in the second screenshot) of swap which is incidental and trivial.

Cached memory is free memory that has been filled with the contents of blocks on disk. It will be vacated as soon as the space is needed by anything else. This is a good thing that enhances performance.

Compare your question with Server refuses to use swap partition.

As for why a server might swap data instead of releasing cache, it may be the case that your cached data was being read much more than your data stored in memory. Programs sometimes have pages that they rarely, if ever, visit. That space is better utilized by caching.

The vm.swappiness setting (also modifiable live through /proc...) will affect that, but spend some time looking closely at what's going on before adjusting it, particularly with your swap in / out counters. sar and atop are useful tools for this.

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  • Thanks, after lot's of testing we found that you were right. Many thanks for your input! Commented Aug 9, 2012 at 15:01
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Try to add vm.swappiness = 0 to /etc/sysctl.conf and run sysctl -p then, this will instruct kernel to release memory occupied by the file cache more aggressively if a user application requires a memory region from kernel.

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  • Thanks for the fast answer, I will test it when the server will be idle. Commented Aug 8, 2012 at 15:46

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