Re: [Xen-devel] LVM Snapshot Troubles

[Michael Vrable <mvrable@xxxxxxxxxxx>]

I've been looking into the LVM snapshot/memory allocation troubles and
will try to come up with a fix.

FYI: In doing more searching for information about the problem, I did
come across this:
    http://www.redhat.com/archives/dm-devel/2004-January/msg00068.html

    "The problem seems to be that dm-ioctl-v4.c sets the PF_MEMALLOC
    flag for the current process.

    Lookaing at the memory allocator (__alloc_page) this means that the
    VM will think the memory allocation is already running (and this is
    a recursion) so it will not try to free pages / rebalance page or
    whatever." ...

I'm looking into sharing memory between the snapshots instead of giving
each snapshot its own private allocation of pages for I/O.  (As I'd like
to scale to a large number of snapshots, and don't want to need >1 MB of
kernel memory per snapshot.)

--Michael Vrable


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