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List:       linux-btrfs
Subject:    Re: btrfs-transacti hangs system for several seconds every few minutes
From:       Zygo Blaxell <ce3g8jdj () umail ! furryterror ! org>
Date:       2020-03-31 4:04:40
Message-ID: 20200331040440.GH2693 () hungrycats ! org
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On Mon, Mar 30, 2020 at 04:14:46PM -0600, Chris Murphy wrote:
> On Sun, Mar 29, 2020 at 12:42 AM Zygo Blaxell
> <ce3g8jdj@umail.furryterror.org> wrote:
> >
> > 90 seconds sounds about right for the block group scan when mounting on
> > a 10TB filesystem.  There's a feature called block group tree in kernel
> > 5.5 that helps with that:  it lays out block group items on disk closer
> > together so they can be read in milliseconds.  This is an on-disk format
> > change, so once you enable that feature, you wouldn't be able to mount
> > the filesystem on an older kernel.  This can be a problem if your
> > sound drivers have regressions.  You might want to wait a few kernel
> > releases to be sure you don't need to downgrade.
> 
> I'm not seeing anything about block group tree in btrfs/super.c.
> 
> There is block_group_cache_tree but I'm not seeing anything about it
> in 'man 5 btrfs' using btrfs-progs 5.4, or in the devel branch.
> 
> So I'm not sure what mount option or btrfstune option this would be,
> seems to be automatic?
> https://github.com/kdave/btrfs-progs/commit/2eaf862f46b3ccb6b7248a0417ebf7096bc93b80

Sorry, my mistake...it was in one of the misc-next branches, but seems to
have been dropped.  Maybe not finished yet?

> 
> --
> Chris Murphy
> 
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