Hi,
I noticed during a rsync based backup on one of my larger Debian12
BaclupPC client host a high CPU usage 20%) of the kswapd. After digging
deeper I noticed it is doing some sort of throwing away "old" filesystem
cache blocks to cache the recent read blocks.
In this scenarion, this does not make sense as th directory in question
is a very stable and very less read directory- mostly just read by
BackupPC. Unfortunately I is veryl large in size (around 400GB). So when
BackupPC is doing a backup the kswapd throws away the current cache to
free it for the to-be-backed-up directory. The blocks are read only once
and after this thrown away a couple of hours later when the default
workload kicks in.
So it does not make sense to keep this in cache and waste thememory for
the real cache. As you can not (afaik) disable caching for a directory I
figured out there is a program which might be helpful. On Debian 12 it
is simply called "nocache".
So I edited my "RsyncClientPath" and set it to "/usr/bin/nocache
/usr/bin/rsync".
Now the blocks read during backup are not going into the cache and the
cache does not get polluted and is keept for proper workload.
So what do you think? Is this a good solution? Or are there any pitfalls?
Greetings
/CV
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