Re: freezes during snapshot creation/deletion -- to be expected? (Was: Re: btrfs based backup?)

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Am Do., 21. Nov. 2019 um 23:22 Uhr schrieb Zygo Blaxell
<ce3g8jdj@xxxxxxxxxxxxxxxxxxxxx>:
> Snapshot delete is pretty aggressive with IO [...]  can effectively hang for a few minutes
> while btrfs-cleaner runs.

It's doesn't look like it's btrfs-cleaner that blocks here, though,
more like it's btrfs-transacti.

> Snapshot create has unbounded running time on 5.0 kernels.

It looks to me like delete, not create, is the culprit here.

> Anything that needs to take a sb_writer lock (which is almost everything
> that modifies the filesystem) will hang until the snapshot create is done;

It's not just fs activity, either. Even if I'm just typing in
LibreOffice or at a bash prompt, the input isn't registered during the
freeze (it's buffered, so it comes out all at once in the end).

Cheers,
C.



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