linux-ext4 - Re: [RFC] Parallelize IO for e2fsck

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Message-id: <20080122070511.GN3180@webber.adilger.int>
Date:	Tue, 22 Jan 2008 00:05:11 -0700
From:	Andreas Dilger <adilger@....com>
To:	David Chinner <dgc@....com>
Cc:	Valerie Henson <val@...consulting.com>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
	Andreas Dilger <adilger@...sterfs.com>,
	Ric Wheeler <ric@....com>
Subject: Re: [RFC] Parallelize IO for e2fsck

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.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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