How do I free swap

[Bryan O'Neal]

Thanks but I may not have made the goal clear, or I miss understand
the instructions. The app is stuffing certain data into swap. The use
case does not see enough of a performance increase to warrant the non
technical result of high swap usage. Adding swap, moving swap etc does
not resolve the issue. I need to flush swap without shutting down the
process consuming 42 of the 48Gb of ram on the box. Once flushed I can
set swapiness to something low.

On 11/4/10, Lisa Kachold <lisakachold at obnosis.com> wrote:
> On Thu, Nov 4, 2010 at 5:58 PM, Bryan O'Neal <
> Bryan.ONeal at theonealandassociates.com> wrote:
>
>> Setting swapiness is how I can deal with a recurrence but it will not
>> flush current swap. And I can not shut down any process to perform
>> swap off. :(
>>
>> On 11/4/10, Eric Shubert <ejs at shubes.net> wrote:
>> > On 11/04/2010 03:26 PM, Bryan O'Neal wrote:
>> >> Please no debates on why I need to clear swap...
>> >>
>> >> If I have a box with 20% free ram and 5% free swap but no paging
>> >> activity - how do I force linux to release the allocated swap? I have
>> >> ~ 2x as much allocated swap as free memory so simply turning swap off
>> >> seems like a bad idea.
>> >>
>> >> Thanks
>> >>
>> >
>> > To minimize swap use, put
>> > vm.swappiness = 0
>> > in /etc/sysctl.conf file. You can also change it on the fly in the
>> > /proc/sys/vm/swappiness.
>> > See http://unixfoo.blogspot.com/2007/11/linux-performance-tuning.html
>> >
>> > AFA purging the swap file is concerned, I only know to stop and start it
>> > again:
>> > # swapoff -a && swapon -a
>> > You might not run into trouble doing this, as there's probably a good
>> > deal of (filesystem) cached ram being used that the kernel will give up
>> > if it's needed for running processes. Do the math though to be sure you
>> > won't run out. Either that or stop some less important processes while
>> > you do it.
>> >
>> > --
>> > -Eric 'shubes'
>> >
>>
>>
> I would leave the current swap, in case you start thrashing, however, you
> requested we not debate, here's the howto:
>
> Type following command to create 512MB swap file (1024 * 512MB = 524288
> block size):
>
> # dd if=/dev/zero of=/swapfile1 bs=1024 count=524288
>
> c) Set up a Linux swap area:
> # mkswap /swapfile1
>
> d) Activate /swapfile1 swap space immediately:
> # swapon /swapfile1
>
> e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab
> file. Open this file using text editor such as vi:
> # vi /etc/fstab
>
> Append following line:
> /swapfile1 swap swap defaults 0 0
> And comment out the old swapfile.  You can swapoff the old file also, but I
> would, in a production machine test the full swap utilization after changes
> through a reboot.
>
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