On Fri, Jun 5, 2020 at 7:09 AM Peter Robinson <pbrobinson@xxxxxxxxx> wrote:
>
> > On 05.06.2020 12:50, Igor Raits wrote:
> > > It does not work in some cases even today anyway.
> >
> > Okay, then the second point - zram will will cause a huge memory
> > fragmentation and significantly decrease overall performance.
>
> Have you got proof of that and can provide figures? Having been
> running it on Arm and IoT by default for a few releases now it
> certainly doesn't cause fragmentation, it's allocated early in the
> boot process so it's one single block. I also run zram on my laptop
> and it's generally faster as when it has to hit swap that's backed by
> RAM and is an order of magnitude faster, even with dealing with
> compression, than hitting my NVME SSD.
With one exception, I agree with all of this including better swap
performance than on NVMe (~1500M/s).
/dev/zram0 is definitely not preallocated
$ cat /sys/block/zram0/mm_stat
4096 74 12288 0 12288 0 0 0
$ zramctl
NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lzo-rle 3.9G 4K 74B 12K 8 [SWAP]
]$
This 4G /dev/zram0 device isn't being used by swap right now.
>From the kernel documentation:
mem_used_total the amount of memory allocated for this disk. This
includes allocator fragmentation and metadata overhead,
allocated for this disk. So, allocator space efficiency
can be calculated using compr_data_size and this statistic.
--
Chris Murphy
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