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Date:      Sun, 03 Jul 2005 01:25:39 -0000
From:      Xin LI <delphij@delphij.net>
To:        David Schultz <das@FreeBSD.ORG>
Cc:        cvs-src@FreeBSD.ORG, src-committers@FreeBSD.ORG, Xin LI <delphij@FreeBSD.ORG>, cvs-all@FreeBSD.ORG
Subject:   Re: cvs commit: src/sbin/fsck_ffs fsck.h pass5.c src/sys/ufs/ffs ffs_alloc.c ffs_softdep.c fs.h
Message-ID:  <1108955636.624.16.camel@spirit>
In-Reply-To: <20050220231711.GA8172@VARK.MIT.EDU>
References:  <200502200802.j1K82G2M003470@repoman.freebsd.org> <20050220231711.GA8172@VARK.MIT.EDU>

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=E5=9C=A8 2005-02-20=E6=97=A5=E7=9A=84 18:17 -0500=EF=BC=8CDavid Schultz=E5=
=86=99=E9=81=93=EF=BC=9A
> >   Since the summary is already re-sync'ed every 30 second, we will
> >   not lag behind too much after a crash.  With this consideration
> >   in mind, it is more reasonable to transfer the responsibility to
> >   background fsck, to reduce the delay after a crash.
>=20
> I'm not sure that I completely buy this explanation.  If an
> application has a 1 GB temporary file open and unlinked at the
> time of the crash, then upon reboot, this change will make it seem
> as though I have 1 GB less space than I really do.  This could
> lead to spurious disk full errors.  (Or will that happen anyway if
> bgfsck hasn't recomputed all the free block bitmaps yet?)

Hmm...   Maybe we should add some constraint on this, for example, for
volumes that fssize < 20G do the recomputation at mount time, despite
the vfs.ffs.compute_summary_at_mount setting?  I think the situation
only happens when bgfsck have not finished the scan yet, and on smaller
volumes, this should not affect so much (after all, we can always set
vfs.ffs.compute_summary_at_mount =3D 1 to restore the old behavior).

Should I send a HEADSUP / update UPDATING so more people will know the
change?

> I don't mean to suggest that this is a bad idea; to the contrary,
> I think it's a great idea.  But unless I'm missing something, it
> has larger adverse effects than claimed in the commit message.
>=20
> FWIW, I run bgfsck on my development box once a month from a cron
> job, rather than after every crash.  As long as there's free space
> and no bugs in the filesystem or I/O system (okay, a big assumption),
> this doesn't hurt anything and saves me lots of time.

Cheers,
--=20
Xin LI <delphij delphij net>  http://www.delphij.net/

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