Date: Tue, 19 Dec 2023 13:23:31 +0000 From: void <void@f-m.fm> To: freebsd-fs@freebsd.org Subject: Re: measuring swap partition speed Message-ID: <ZYGZUw61CD3hIwKM@int21h> In-Reply-To: <CANCZdfpgvE8UjX1XUgimbotpnrH-fXYWZU3kfAwD849bMrT2Vg@mail.gmail.com> References: <ZXxis23iKT3iHDdt@int21h> <CANCZdfpgvE8UjX1XUgimbotpnrH-fXYWZU3kfAwD849bMrT2Vg@mail.gmail.com>
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On Fri, Dec 15, 2023 at 08:41:10AM -0700, Warner Losh wrote:
>benchmarking of storage. Do a random workload with a 8k write size (since
>that's the page
>size of aarch64) on one of the swap partitions when it's not in active use.
I've not got my head around benchmarks/fio yet. But I've done the following
tests which seem to show abysmal swap speed, not linked to the hardware :
# dd if=/dev/urandom of=/dev/da0p4 bs=8k count=250000 conv=sync status=progress
^C11862016 bytes (12 MB, 11 MiB) transferred 40.063s, 296 kB/s
1494+0 records in
1493+0 records out
12230656 bytes transferred in 41.495178 secs (294749 bytes/sec)
# dd if=/dev/urandom of=/dev/da0p4 bs=128k count=250000 conv=sync status=progress
^C88080384 bytes (88 MB, 84 MiB) transferred 47.309s, 1862 kB/s
674+0 records in
673+0 records out
88211456 bytes transferred in 48.677246 secs (1812170 bytes/sec)
But when the same partition is formatted as ufs:
# newfs -U /dev/da0p4
/dev/da0p4: 2048.0MB (4194304 sectors) block size 32768, fragment size 4096
using 4 cylinder groups of 512.03MB, 16385 blks, 65664 inodes.
with soft updates
super-block backups (for fsck_ffs -b #) at:
192, 1048832, 2097472, 3146112
# mount /dev/da0p4 /mnt
# dd if=/dev/urandom of=/mnt/test8k.bin bs=8k count=250000 conv=sync status=progress
2036400128 bytes (2036 MB, 1942 MiB) transferred 18.013s, 113 MB/s
250000+0 records in
250000+0 records out
2048000000 bytes transferred in 18.084497 secs (113246167 bytes/sec)
why the difference?
My non-expert observation is that when swap gets used, all writes start backing up and
it starts thrashing. it's a thing I'd expect to see with slow media like microSD but
not on faster hardware.
I have the following sysctls set to minimise swap use
vm.pageout_oom_seq=120
vm.pfault_oom_attempts=-1
vm.pageout_update_period=0
vfs.zfs.arc.min=536870912
vfs.zfs.arc_max=1073741824
this is a rpib4 with 8GB
how can I fix?
--
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