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Date:	Tue, 22 Jan 2008 19:16:39 +1100
From:	David Chinner <>
To:	David Chinner <>,
	Valerie Henson <>,,,, "Theodore Ts'o" <>,
	Andreas Dilger <>,
	Ric Wheeler <>
Subject: Re: [RFC] Parallelize IO for e2fsck

On Tue, Jan 22, 2008 at 12:05:11AM -0700, Andreas Dilger wrote:
> On Jan 22, 2008  14:38 +1100, David Chinner wrote:
> > On Mon, Jan 21, 2008 at 04:00:41PM -0700, Andreas Dilger wrote:
> > > I discussed this with Ted at one point also.  This is a generic problem,
> > > not just for readahead, because "fsck" can run multiple e2fsck in parallel
> > > and in case of many large filesystems on a single node this can cause
> > > memory usage problems also.
> > > 
> > > What I was proposing is that "fsck.{fstype}" be modified to return an
> > > estimated minimum amount of memory needed, and some "desired" amount of
> > > memory (i.e. readahead) to fsck the filesystem, using some parameter like
> > > "fsck.{fstype} --report-memory-needed /dev/XXX".  If this does not
> > > return the output in the expected format, or returns an error then fsck
> > > will assume some amount of memory based on the device size and continue
> > > as it does today.
> > 
> > And while fsck is running, some other program runs that uses
> > memory and blows your carefully calculated paramters to smithereens?
> Well, fsck has a rather restricted working environment, because it is
> run before most other processes start (i.e. single-user mode).  For fsck
> initiated by an admin in other runlevels the admin would need to specify
> the upper limit of memory usage.  My proposal was only for the single-user
> fsck at boot time.

The simple case. ;)

Because XFS has shutdown features, it's not uncommon to hear about
people running xfs_repair on an otherwise live system. e.g. XFS
detects a corrupted block, shuts down the filesystem, the admin
unmounts it, runs xfs_repair, puts it back online. meanwhile, all
the other filesystems and users continue unaffected. In this use
case, getting feedback about memory usage is, IMO, very worthwhile.


Dave Chinner
Principal Engineer
SGI Australian Software Group
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