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Re: [Xen-devel] LVM Snapshot Troubles

To: Michael Vrable <mvrable@xxxxxxxxxxx>
Subject: Re: [Xen-devel] LVM Snapshot Troubles
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Tue, 28 Sep 2004 21:06:59 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
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> On Tue, Sep 28, 2004 at 04:43:25PM +0100, Ian Pratt wrote:
> > 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.
> When I've run into memory trouble with snapshots, I've always seen a
> stack backtrace that points me at kcopyd_client_create.  Following the
> code: when creating a snapshot, a new kcopyd client is created with 256
> (SNAPSHOT_PAGES in dm-snap.c) pages (= 1 MB) dedicated to that snapshot.
> I think I managed to dig up the logs from one of the failures I've seen;
> I've attached them to this message.

It might be worth adding "| __GFP_REPEAT" to the alloc_page in 

If this fixes things, we could probably get the patch accepted
into mainline Linux.

(Of course, GFP_REPEAT may be a nop under Linux's VM...)


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