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    SubjectRe: [Ext2-devel] Re: [RFC][PATCH 0/2]Extend ext3 filesystem limit from 8TB to 16TB
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    On Mon, 2006-04-10 at 11:11 +0200, Laurent Vivier wrote:
    > Le jeu 30/03/2006 à 03:54, Andrew Morton a écrit :
    > > Mingming Cao <cmm@us.ibm.com> wrote:
    > > >
    > > > The things need to be done to complete this work is the issue with
    > > > current percpu counter, which could not handle u32 type count well.
    > >
    > > I'm surprised there's much of a problem here. It is a 32-bit value, so it
    > > should mainly be a matter of treating the return value from
    > > percpu_counter_read() as unsigned long.
    > >
    > > However a stickier problem is when dealing with a filesystem which has,
    > > say, 0xffff_ff00 blocks. Because percpu counters are approximate, and a
    > > counter which really has a value of 0xffff_feee might return 0x00000123.
    > > What do we do then?
    > >
    > > Of course the simple option is to nuke the percpu counters in ext3 and use
    > > atomic_long_t (which is signed, so appropriate treat-it-as-unsigned code
    > > would be needed). I doubt if the percpu counters in ext3 are gaining us
    > > much.
    >
    > I tried to make something in this way.
    > Does the attached patch look like the thing you though about ?
    >

    I tried the other way -- I am trying to keep the percpu counter in use
    in ext2/3 as much as possible. I proposed a fix for percpu counter to
    deal with the possible "overflow" (i.e, a counter really has a value of
    0xfff_feee and after updating one local counter it truens 0x00000123).
    Will send the proposed patch out for review and comments soon.

    Mingming

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