[pve-devel] [RFC PATCH pve-cluster] fix #5728: pmxcfs: allow bigger writes than 4k for fuse

[Thomas Lamprecht]

Am 19/09/2024 um 11:52 schrieb Dominik Csapak:
> by default libfuse2 limits writes to 4k size, which means that on writes
> bigger than that, we do a whole write cycle for each 4k block that comes
> in. To avoid that, add the option 'big_writes' to allow writes bigger
> than 4k at once.
> 
> This should improve pmxcfs performance for situations where we often
> write large files (e.g. big ha status) and maybe reduce writes to disk.

Should? Something like before/after for benchmark numbers, flamegraphs
would be really good to have, without those it's rather hard to discuss
this, and I'd like to avoid having to do those, or check the inner workings
of the affected fuse userspace/kernel code paths here myself.

> 
> If we'd change to libfuse3, this would be a non-issue, since that option
> got removed and is the default there.

I'd prefer that. At least if done with the future PVE 9.0, as I do not think
it's a good idea in the middle of a stable release cycle.

FWIW, some Debian Devs also want to push the fuse 2 to 3 migration forward
[0]. So, sooner or later we have to switch over pmxcfs anyway, and there's
already a POC from Fabian [1].

[0]: https://lists.debian.org/debian-devel/2024/08/msg00177.html
[1]: https://lore.proxmox.com/pve-devel/20220715074742.3387301-1-f.gruenbichler@proxmox.com/