My swapdisk can write 100 MB/s. When the system swaps out it only writes 8-20 MB/s.
iostat says the device is 100% active, so I have the feeling that Linux is seeking on the drive or swapping out small chunks.
I could explain this if there were swap-ins at the same time, but there are no swap-ins and no other disk I/O.
Is it possible for me to tell Linux to swap out in bigger contiguous chunks, say, determining the oldest 10 MB pages and swap them out in one chunk?
A bit like saying the page frame size of swap is not 4K but 10M.
For my system I think an algorithm along the lines of this would be ideal:
dirty_pct = dirty pages / all RAM if dirty_pct > 50%: # Half of memory is dirty, slowly start swapping out if busy_time(swapdevice) < dirty_pct: # if RAM is 60% dirty, start swapping if disk is less than 60% busy # if RAM is 90% dirty, start swapping if disk is less than 90% busy identify the next 10 MB that would be swapped if dirty_pct had been 100% save the 10 MB to swap as a single chunk mark the pages as clean
This way my system would start swapping out at 50% dirty and it would not affect performance, because it would do so on a drive that was sitting idle anyway. Maybe the swapped data will never be used, and then we wasted some IO that was sitting idle anyway.
$ uname -a Linux r815 4.15.0-99-generic #100-Ubuntu SMP Wed Apr 22 20:32:56 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
zswapand that does nothing for swapping faster to disk. It compresses to RAM, but when it runs out of RAM it starts swapping to disk, too. And that is the situation I am in.
iostat says the device is 100% active, so I have the feeling that Linux is seeking on the drive or swapping out small chunksHDDs can only serve about 80-150 IOPS so if the request queue is already full the performance will be capped at that point. If each request only reads a tiny amount of blocks then you won't be able to achieve the maximum speed. SSD can achieve 150000-500000 IOPS so it'll be better. Without SSD on Windows there's ReadyBoost which utilizes the low access time of USB flash drives or SD cards but there's nothing like that on Linux