Re: Proposal to enable WAPBL by default for 10.0

[David Holland <dholland-tech%netbsd.org@localhost>]

On Sun, Jul 26, 2020 at 11:20:37PM +0000, maya%NetBSD.org@localhost wrote:
 > > To be explicit:
 > > 
 > > It is the same underly problem either way, and it is worse in practice
 > > with WAPBL than without because WAPBL ffs runs faster than non-WAPBL
 > > ffs and thus accumulates more unwritten blocks.
 > 
 > It looks like this difference is because FFS doesn't flush the disk
 > cache often, but if WAPBL is enabled, it does on every log write.

That would cause WAPBL to generate fewer unwritten blocks, which isn't
consistent with the observed results. (Or maybe it is, and without
this effect WAPBL would be even worse.)

But this is unlikely to be an issue in most cases, because data that
makes it to the disk-level cache is not lost just because the kernel
panics. You have to turn off the power for that.

-- 
David A. Holland
dholland%netbsd.org@localhost