5.4.60 uksm doesn't save the memory for KVM images

[hailumeng]

I have launched 4 same type of KVM images in Ubuntu 20.04 patched with 5.4.60 uksm. The memory saving is only 4%. Tested with other different KVM images, the saving is around 50%. I also find out the non-working KVM does use 5.15.38 kernel. Maybe I need Ubuntu 22.04 to host this KVM with uksm-5.15.patch? Any guidance? Thank you.

[bhzhu203]

You could disable memory randomize in newly kernel

echo 0 > /proc/sys/kernel/randomize_va_space

[hailumeng]

Thank you bhzhu203 for the advice here. Before I give it a try, do you have any other recommendations for tuning? The reason I’m asking is the guest VM I have uses 18G memory each. When testing with them, the saving is much less compared to the VM which only has 4 or 8G memory. I wonder if I need to tune uksm to work on big memory VM. Thoughts? Thank you!

[bhzhu203]

Thank you bhzhu203 for the advice here. Before I give it a try, do you have any other recommendations for tuning? The reason I’m asking is the guest VM I have uses 18G memory each. When testing with them, the saving is much less compared to the VM which only has 4 or 8G memory. I wonder if I need to tune uksm to work on big memory VM. Thoughts? Thank you!

You could try to use zram and save some memory of cache (compresion)

echo 3G >  /sys/block/zram0/disksize
mkswap  /dev/zram0
swapon --priority 100 /dev/zram0

cat /sys/block/zram0/comp_algorithm
lzo [lzo-rle] lz4 lz4hc 842 zstd (lzo-rle better)

#then flush the cache quickly

cat /etc/sysctl.conf

vm.min_free_kbytes=162164 # 1% total memory in M
vm.dirty_background_ratio=5
vm.dirty_ratio = 10
vm.dirty_expire_centisecs = 1500
vm.dirty_writeback_centisecs = 300
vm.vfs_cache_pressure=150
vm.swappiness=85

[bhzhu203]

how about the randomize_va_space option now？

[hailumeng]

Thank you bhzhu203. randomize_va_space didn’t make much difference at all. I’ll try these setting you mentioned above. Thank you so much for the help!

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On Fri, Aug 5, 2022 at 3:31 AM bhzhu203 ***@***.***> wrote: how about the randomize_va_space option now？ — Reply to this email directly, view it on GitHub <#82 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AD4HJQ4RV3RGQDE4IZG7NELVXTGMRANCNFSM542BQ5NA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[hailumeng]

I also wonder if there is any pages_to_scan setting like ksm I can tweak since the memory required for VM is around 20G. It’s a lot of pages to scan.

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On Fri, Aug 5, 2022 at 7:21 AM Hailu Meng ***@***.***> wrote: Thank you bhzhu203. randomize_va_space didn’t make much difference at all. I’ll try these setting you mentioned above. Thank you so much for the help! On Fri, Aug 5, 2022 at 3:31 AM bhzhu203 ***@***.***> wrote: > how about the randomize_va_space option now？ > > — > Reply to this email directly, view it on GitHub > <#82 (comment)>, or > unsubscribe > <https://github.com/notifications/unsubscribe-auth/AD4HJQ4RV3RGQDE4IZG7NELVXTGMRANCNFSM542BQ5NA> > . > You are receiving this because you authored the thread.Message ID: > ***@***.***> >