Why does RHEL use swap even when vm.swappiness = 1?Why does swappiness not work?real memory usageWhat does the vm.swappiness parameter really control?Why is swap used when a lot of memory is still free?Expand the size of swap partitionWhen does the swap get emptied, after being used?Why QEMU can't use the linux memory buffers memory?Linux: When time to upgrade RAMMake or force tmpfs to swap before the file cacheExplanation for “page allocation failure” kernel messageHow shall I understand the output of free?

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Why does RHEL use swap even when vm.swappiness = 1?


Why does swappiness not work?real memory usageWhat does the vm.swappiness parameter really control?Why is swap used when a lot of memory is still free?Expand the size of swap partitionWhen does the swap get emptied, after being used?Why QEMU can't use the linux memory buffers memory?Linux: When time to upgrade RAMMake or force tmpfs to swap before the file cacheExplanation for “page allocation failure” kernel messageHow shall I understand the output of free?













2















RHEL 7.2 memory use, per free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13383 2936 16381


we see that used swap is 2936M



so we want to decrease it to min by the following



echo 1 > /proc/sys/vm/swappiness

sysctl -w vm.swappiness=1

echo "vm.swappiness = 1" >> /etc/sysctl.conf


and after 10 min we check again , but still OS used the swap



free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13389 2930 16381


why the actions that we did not take affect immeditly?



Do we need to restart the OS, in order to get swap used to be 0 ?



example



we run vmstat:



 vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0


we decrease the vm.swappiness=1



and run vmstat after 10min:



procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0









share|improve this question



















  • 1





    Do you know for a fact that Linux would empty the swap when you set swappiness to 1? Because what you are showing is that it does not use further swap space.

    – Kusalananda
    yesterday






  • 1





    so you have a total 384GB of RAM according to free; since that is not enough to make a system run... RH 15244 => 1.5 x RAM is over 500gb, better go get a second disk and make the whole thing swap

    – ron
    13 hours ago
















2















RHEL 7.2 memory use, per free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13383 2936 16381


we see that used swap is 2936M



so we want to decrease it to min by the following



echo 1 > /proc/sys/vm/swappiness

sysctl -w vm.swappiness=1

echo "vm.swappiness = 1" >> /etc/sysctl.conf


and after 10 min we check again , but still OS used the swap



free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13389 2930 16381


why the actions that we did not take affect immeditly?



Do we need to restart the OS, in order to get swap used to be 0 ?



example



we run vmstat:



 vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0


we decrease the vm.swappiness=1



and run vmstat after 10min:



procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0









share|improve this question



















  • 1





    Do you know for a fact that Linux would empty the swap when you set swappiness to 1? Because what you are showing is that it does not use further swap space.

    – Kusalananda
    yesterday






  • 1





    so you have a total 384GB of RAM according to free; since that is not enough to make a system run... RH 15244 => 1.5 x RAM is over 500gb, better go get a second disk and make the whole thing swap

    – ron
    13 hours ago














2












2








2








RHEL 7.2 memory use, per free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13383 2936 16381


we see that used swap is 2936M



so we want to decrease it to min by the following



echo 1 > /proc/sys/vm/swappiness

sysctl -w vm.swappiness=1

echo "vm.swappiness = 1" >> /etc/sysctl.conf


and after 10 min we check again , but still OS used the swap



free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13389 2930 16381


why the actions that we did not take affect immeditly?



Do we need to restart the OS, in order to get swap used to be 0 ?



example



we run vmstat:



 vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0


we decrease the vm.swappiness=1



and run vmstat after 10min:



procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0









share|improve this question
















RHEL 7.2 memory use, per free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13383 2936 16381


we see that used swap is 2936M



so we want to decrease it to min by the following



echo 1 > /proc/sys/vm/swappiness

sysctl -w vm.swappiness=1

echo "vm.swappiness = 1" >> /etc/sysctl.conf


and after 10 min we check again , but still OS used the swap



free -m:



 total used free shared buff/cache available
Mem: 386564 77941 57186 687 251435 306557
Swap: 13389 2930 16381


why the actions that we did not take affect immeditly?



Do we need to restart the OS, in order to get swap used to be 0 ?



example



we run vmstat:



 vmstat
procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0


we decrease the vm.swappiness=1



and run vmstat after 10min:



procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
3 0 85740 20255872 2238248 183126400 0 0 7 162 0 0 7 1 92 0 0






rhel kernel memory swap






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 14 hours ago









GAD3R

27.5k1858114




27.5k1858114










asked yesterday









yaelyael

2,78132777




2,78132777







  • 1





    Do you know for a fact that Linux would empty the swap when you set swappiness to 1? Because what you are showing is that it does not use further swap space.

    – Kusalananda
    yesterday






  • 1





    so you have a total 384GB of RAM according to free; since that is not enough to make a system run... RH 15244 => 1.5 x RAM is over 500gb, better go get a second disk and make the whole thing swap

    – ron
    13 hours ago













  • 1





    Do you know for a fact that Linux would empty the swap when you set swappiness to 1? Because what you are showing is that it does not use further swap space.

    – Kusalananda
    yesterday






  • 1





    so you have a total 384GB of RAM according to free; since that is not enough to make a system run... RH 15244 => 1.5 x RAM is over 500gb, better go get a second disk and make the whole thing swap

    – ron
    13 hours ago








1




1





Do you know for a fact that Linux would empty the swap when you set swappiness to 1? Because what you are showing is that it does not use further swap space.

– Kusalananda
yesterday





Do you know for a fact that Linux would empty the swap when you set swappiness to 1? Because what you are showing is that it does not use further swap space.

– Kusalananda
yesterday




1




1





so you have a total 384GB of RAM according to free; since that is not enough to make a system run... RH 15244 => 1.5 x RAM is over 500gb, better go get a second disk and make the whole thing swap

– ron
13 hours ago






so you have a total 384GB of RAM according to free; since that is not enough to make a system run... RH 15244 => 1.5 x RAM is over 500gb, better go get a second disk and make the whole thing swap

– ron
13 hours ago











2 Answers
2






active

oldest

votes


















8














As you’ve been told before (see Why does swappiness not work?), changing swappiness only affects future decisions made by the kernel when it needs to free memory. Reducing it won’t cause the kernel to reload everything that’s been swapped out.



Your vmstat output shows that swap isn’t being actively used, i.e. your current workloads really don’t need the pages which have been swapped out.



There’s no point in trying to micro-manage the kernel’s use of swap in the way you tend to do. Depending on your workload, decide whether you need to favour the page cache or not, adjust swappiness accordingly, then leave the system to run.



If you really want to clear swap, disable it and re-enable it:



swapoff -a && swapon -a





share|improve this answer






























    3














    free -m is not a reliable source of information about swap use. Instead, please use vmstat before and after the echo commands which temporarily change swappiness.



    1) swapoff -a && swapon -a && vmstat

    2) do work which requires swapping

    3) vmstat



    Now you know how much swapping is going on before changing the swappiness. If there's no swapping going on, find other jobs which do swap.



    4) use and echo command to change swappiness temporarily

    5) swapoff -a && swapon -a && vmstat

    6) do work which requires swapping

    7) vmstat



    8) compare the si and so values.



    The values to watch are:



    si: Amount of memory swapped in from disk (/s).
    so: Amount of memory swapped to disk (/s).


    You may also find helpful information in the RHEL 7 Performance Tuning Guide.



    Many thanks to Stephen Kitt for reminding me about swapon and swapoff.






    share|improve this answer

























    • when I run vmstat under swap I see 2224 , this is the swap that OS used?

      – yael
      yesterday












    • any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

      – yael
      yesterday











    • I add example of vmstat before and after , as you can see the value are the same - how it can be

      – yael
      yesterday











    • si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

      – K7AAY
      yesterday











    Your Answer








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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    8














    As you’ve been told before (see Why does swappiness not work?), changing swappiness only affects future decisions made by the kernel when it needs to free memory. Reducing it won’t cause the kernel to reload everything that’s been swapped out.



    Your vmstat output shows that swap isn’t being actively used, i.e. your current workloads really don’t need the pages which have been swapped out.



    There’s no point in trying to micro-manage the kernel’s use of swap in the way you tend to do. Depending on your workload, decide whether you need to favour the page cache or not, adjust swappiness accordingly, then leave the system to run.



    If you really want to clear swap, disable it and re-enable it:



    swapoff -a && swapon -a





    share|improve this answer



























      8














      As you’ve been told before (see Why does swappiness not work?), changing swappiness only affects future decisions made by the kernel when it needs to free memory. Reducing it won’t cause the kernel to reload everything that’s been swapped out.



      Your vmstat output shows that swap isn’t being actively used, i.e. your current workloads really don’t need the pages which have been swapped out.



      There’s no point in trying to micro-manage the kernel’s use of swap in the way you tend to do. Depending on your workload, decide whether you need to favour the page cache or not, adjust swappiness accordingly, then leave the system to run.



      If you really want to clear swap, disable it and re-enable it:



      swapoff -a && swapon -a





      share|improve this answer

























        8












        8








        8







        As you’ve been told before (see Why does swappiness not work?), changing swappiness only affects future decisions made by the kernel when it needs to free memory. Reducing it won’t cause the kernel to reload everything that’s been swapped out.



        Your vmstat output shows that swap isn’t being actively used, i.e. your current workloads really don’t need the pages which have been swapped out.



        There’s no point in trying to micro-manage the kernel’s use of swap in the way you tend to do. Depending on your workload, decide whether you need to favour the page cache or not, adjust swappiness accordingly, then leave the system to run.



        If you really want to clear swap, disable it and re-enable it:



        swapoff -a && swapon -a





        share|improve this answer













        As you’ve been told before (see Why does swappiness not work?), changing swappiness only affects future decisions made by the kernel when it needs to free memory. Reducing it won’t cause the kernel to reload everything that’s been swapped out.



        Your vmstat output shows that swap isn’t being actively used, i.e. your current workloads really don’t need the pages which have been swapped out.



        There’s no point in trying to micro-manage the kernel’s use of swap in the way you tend to do. Depending on your workload, decide whether you need to favour the page cache or not, adjust swappiness accordingly, then leave the system to run.



        If you really want to clear swap, disable it and re-enable it:



        swapoff -a && swapon -a






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered yesterday









        Stephen KittStephen Kitt

        178k24405482




        178k24405482























            3














            free -m is not a reliable source of information about swap use. Instead, please use vmstat before and after the echo commands which temporarily change swappiness.



            1) swapoff -a && swapon -a && vmstat

            2) do work which requires swapping

            3) vmstat



            Now you know how much swapping is going on before changing the swappiness. If there's no swapping going on, find other jobs which do swap.



            4) use and echo command to change swappiness temporarily

            5) swapoff -a && swapon -a && vmstat

            6) do work which requires swapping

            7) vmstat



            8) compare the si and so values.



            The values to watch are:



            si: Amount of memory swapped in from disk (/s).
            so: Amount of memory swapped to disk (/s).


            You may also find helpful information in the RHEL 7 Performance Tuning Guide.



            Many thanks to Stephen Kitt for reminding me about swapon and swapoff.






            share|improve this answer

























            • when I run vmstat under swap I see 2224 , this is the swap that OS used?

              – yael
              yesterday












            • any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

              – yael
              yesterday











            • I add example of vmstat before and after , as you can see the value are the same - how it can be

              – yael
              yesterday











            • si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

              – K7AAY
              yesterday
















            3














            free -m is not a reliable source of information about swap use. Instead, please use vmstat before and after the echo commands which temporarily change swappiness.



            1) swapoff -a && swapon -a && vmstat

            2) do work which requires swapping

            3) vmstat



            Now you know how much swapping is going on before changing the swappiness. If there's no swapping going on, find other jobs which do swap.



            4) use and echo command to change swappiness temporarily

            5) swapoff -a && swapon -a && vmstat

            6) do work which requires swapping

            7) vmstat



            8) compare the si and so values.



            The values to watch are:



            si: Amount of memory swapped in from disk (/s).
            so: Amount of memory swapped to disk (/s).


            You may also find helpful information in the RHEL 7 Performance Tuning Guide.



            Many thanks to Stephen Kitt for reminding me about swapon and swapoff.






            share|improve this answer

























            • when I run vmstat under swap I see 2224 , this is the swap that OS used?

              – yael
              yesterday












            • any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

              – yael
              yesterday











            • I add example of vmstat before and after , as you can see the value are the same - how it can be

              – yael
              yesterday











            • si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

              – K7AAY
              yesterday














            3












            3








            3







            free -m is not a reliable source of information about swap use. Instead, please use vmstat before and after the echo commands which temporarily change swappiness.



            1) swapoff -a && swapon -a && vmstat

            2) do work which requires swapping

            3) vmstat



            Now you know how much swapping is going on before changing the swappiness. If there's no swapping going on, find other jobs which do swap.



            4) use and echo command to change swappiness temporarily

            5) swapoff -a && swapon -a && vmstat

            6) do work which requires swapping

            7) vmstat



            8) compare the si and so values.



            The values to watch are:



            si: Amount of memory swapped in from disk (/s).
            so: Amount of memory swapped to disk (/s).


            You may also find helpful information in the RHEL 7 Performance Tuning Guide.



            Many thanks to Stephen Kitt for reminding me about swapon and swapoff.






            share|improve this answer















            free -m is not a reliable source of information about swap use. Instead, please use vmstat before and after the echo commands which temporarily change swappiness.



            1) swapoff -a && swapon -a && vmstat

            2) do work which requires swapping

            3) vmstat



            Now you know how much swapping is going on before changing the swappiness. If there's no swapping going on, find other jobs which do swap.



            4) use and echo command to change swappiness temporarily

            5) swapoff -a && swapon -a && vmstat

            6) do work which requires swapping

            7) vmstat



            8) compare the si and so values.



            The values to watch are:



            si: Amount of memory swapped in from disk (/s).
            so: Amount of memory swapped to disk (/s).


            You may also find helpful information in the RHEL 7 Performance Tuning Guide.



            Many thanks to Stephen Kitt for reminding me about swapon and swapoff.







            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited yesterday

























            answered yesterday









            K7AAYK7AAY

            814926




            814926












            • when I run vmstat under swap I see 2224 , this is the swap that OS used?

              – yael
              yesterday












            • any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

              – yael
              yesterday











            • I add example of vmstat before and after , as you can see the value are the same - how it can be

              – yael
              yesterday











            • si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

              – K7AAY
              yesterday


















            • when I run vmstat under swap I see 2224 , this is the swap that OS used?

              – yael
              yesterday












            • any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

              – yael
              yesterday











            • I add example of vmstat before and after , as you can see the value are the same - how it can be

              – yael
              yesterday











            • si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

              – K7AAY
              yesterday

















            when I run vmstat under swap I see 2224 , this is the swap that OS used?

            – yael
            yesterday






            when I run vmstat under swap I see 2224 , this is the swap that OS used?

            – yael
            yesterday














            any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

            – yael
            yesterday





            any I did the procedure on other machine , but vmstat about the swap , and after the procedure are the same values

            – yael
            yesterday













            I add example of vmstat before and after , as you can see the value are the same - how it can be

            – yael
            yesterday





            I add example of vmstat before and after , as you can see the value are the same - how it can be

            – yael
            yesterday













            si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

            – K7AAY
            yesterday






            si and so are the values to look at. Since si and so have not changed, you are not swapping. As per the How To Read Vmstat Output link I provided, "The first line of the report will contain the average values since the last time the computer was rebooted." and not the immediate values.

            – K7AAY
            yesterday


















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