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Re: long hangs when deleting large directories (3.0-rc3)

To: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
Subject: Re: long hangs when deleting large directories (3.0-rc3)
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 20 Jun 2011 12:36:25 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20110620020236.GB1730@xxxxxxxxxxxxxx>
References: <20110618141950.GA1685@xxxxxxxxxxxxxx> <20110619222447.GI561@dastard> <20110620005415.GA1730@xxxxxxxxxxxxxx> <20110620013449.GO561@dastard> <20110620020236.GB1730@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Mon, Jun 20, 2011 at 04:02:36AM +0200, Markus Trippelsdorf wrote:
> On 2011.06.20 at 11:34 +1000, Dave Chinner wrote:
> > On Mon, Jun 20, 2011 at 02:54:15AM +0200, Markus Trippelsdorf wrote:
> > > On 2011.06.20 at 08:24 +1000, Dave Chinner wrote:
> > > > On Sat, Jun 18, 2011 at 04:19:50PM +0200, Markus Trippelsdorf wrote:
> > > > > Running the latest git kernel (3.0-rc3) my machine hangs for long
> > > > > periods (1-2 sec) whenever I delete a large directory recursively on 
> > > > > my
> > > > > xfs partition. During the hang I cannot move the mouse pointer or use
> > > > > the keyboard (but the music keeps playing without stuttering). A quick
> > > > > way to reproduce is to "rm -fr" a kernel tree. 
> > > > 
> > > > So what is the system doing when it "hangs"? Is it CPU bound (e.g.
> > > > cpu scheduler issue)? Is the system running out of memory and
> > > > stalling everything in memory reclaim? What IO is occurring?
> > > 
> > > It's totally idle otherwise; just a desktop with a single xterm. The
> > > machine has four cores (and also runs with "CONFIG_PREEMPT=y"), so I
> > > don't think it is CPU bound at all. It has 8GB of memory (and the
> > > "hangs" even occur after reboot when most of it is free). No other IO
> > > activity is occurring.
> > 
> > Sure, the system might be otherwise idle, but what I was asking is
> > what load does the "rm -rf" cause. What IO does it cause? is it cpu
> > bound? etc.
> 
> I have not measured this, so I cannot tell.

And so you are speculating as to the cause of the problem. What I'm
trying to do is work from the bottom up to ensure that the layers
below the fs are not the cause of the problem.

> > > > Is your partition correctly sector aligned for however your drive
> > > > maps it's 4k sectors?
> > > 
> > > Yes, it's a GPT partition that is aligned to 1MB.
> > 
> > Ok, that is fine, but the big question now is how does the drive
> > align sector 0? Is that 4k aligned, or is it one of those drives
> > that aligns an odd 512 byte logical sector to the physical 4k sector
> > boundary (i.e. sector 63 is 4k aligned to work with msdos
> > partitions). FYI, some drives have jumpers on them to change this
> > odd/even sector alignment configuration.....
> 
> No, it's none of those (it's a Seagate Barracuda Green ST1500). Sector 0
> is 4k aligned for sure. The odd 512 byte offset was present only on some
> first generation drives. 
> But I think the whole alignment issue is a red herring, because I cannot
> reproduce the "hangs" on the next partition on the same drive. This
> partition is larger and contains my music and film collection (so mostly
> static content and no traffic).

Which also means you might have one unaligned and one aligned
partition.  i.e. the test results you have presented does not
necessarily point at a filesystem problem. We always ask for exact
details of your storage subsystem for these reasons - so we can
understand if there's something that you missed or didn't think was
important enough to tell us. You may have already checked those
things, but we don't know that if you don't tell us....

So, is the sector alignment of the second partition the same as the
first partition?

> And as I wrote in my other reply to this
> thread: »it appears that the observed "hangs" are the result of a
> strongly aged file-system.«

There is no evidence that points to any cause. Hell, I don't even
know what you consider a "strongly aged filesystem" looks like....

If the alignment is the cause of the problem, you should be able to
see a difference in performance when doing random 4k synchronous
writes to a large file on differently aligned partitions. Can you
run the same random 4k sync write test on both partitions (make sure
barriers are enabled) and determine if they perform the same?

If the filesystem layout is the cause of the problem, you should be
able to take a metadump of the problematic filesystem, restore it to
a normal 512 sector drive and reproduce the "rm -rf" problem. Can
you try this as well?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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