Re: How to limit amount of virtual memory used for files (was: Re: Tuning ZFS memory usage on NetBSD - call for advice)

[Matthias Petermann <mp%petermann-it.de@localhost>]

Hi,

Am 20.09.2022 um 08:27 schrieb RVP:
> On Tue, 20 Sep 2022, Matthias Petermann wrote:
>
> > I think I had answered this earlier (but I'm not quite sure) - the 
> > problem only occurs when I write the data obtained with "zfs send" to 
> > a local file system (e.g. the USB HDD). If I send the data to a remote 
> > system with netcat instead, the "file usage" remains within the green 
> > range.
> >
> > [...]
> >
> > This raises the question for me: can I somehow limit this kind of 
> > memory use on a process basis?
>
> Try piping to dd with direct I/O:
>
> ... | dd bs=10m oflag=direct of=foo.file
>
> Does that help?

In theory this looked exactly what I was looking for... unfortunately I 
can observe the same effect like I was doing before with the simple 
redirection. "File" grows to a maximum, the system starts to swap.

I use this command line:

```
zfs send -R tank/vol@backup | dd bs=10m oflag=creat,direct 
of=/mnt/vhost-tank-vol.zfs
```

(I had to add the creat flag as the file did not exist before)

The memory remains occupied even if I send a "sync" in between. However, 
it is immediately released again when I a) delete the file or b) unmount 
the file system.

Have I used the direct flag correctly?

Kind regards
Matthias