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Re: [Xen-devel] Automation scripts

To: Peri Hankey <mpah@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Automation scripts
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Tue, 28 Sep 2004 16:43:25 +0100
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, Michael Vrable <mvrable@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
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> It looks as if lvm2 uses quite a lot of memory analysing multiple 
> snapshots of a single origin. I rebooted the dom0 machine and 
> immediately did 'vchange -ay vmspace' which makes the volume group 
> vmspace active. This claims to run out of memory - always so far on one 
> of a list of snapshots of a common origin, but not always on the same 
> one. When it runs out memory adding a new snapshot, it tends to mention 
> one of the other snapshots, and as I have said, the whole caboodle then 
> becomes unusable until after a reboot.

> dm-snapshot-in       128    162     48 
> dm-snapshot-ex     19556  19662     16 
> dm_tio             14336  14464     16 
> dm_io              14336  14464     16 

20,000 dm-snapshot-ex entries sounds like a lot, but they're only
16 bytes each. From looking at the code it looks like it needs to
store the entire exception table in memory rather than using it
as a cache of what's on disk, which is a shame. Still, 50k
x16 bytes is less than 1MB.

There's nothing in slabinfo that looks crazy. I wander where all
your memory is gone? BTW: how big is your dom0? 

It's possible that dm-io or kcopyd is chewing up pages (which
won't show up in the slab allocator). I'm surprised they're not
just transient, though.

Perhaps someone's going to need to take a look at device
mapper. Building a version with debug printk's enabled would be a
good start. I'd like to know what allocation is failing.



Ian


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