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    SubjectRe: [PATCH 1/2] ext3 percpu counter fixes to suppport for more than 2**31 ext3 free blocks counter
    On Mon, Apr 24, 2006 at 10:48:32AM -0700, Mingming Cao wrote:
    > On Fri, 2006-04-21 at 15:09 -0700, Andrew Morton wrote:
    > > >
    > > I think it would be saner to explicitly specify the size of the field.
    > > That means using s32 and s64 throughout this code.
    > >
    >
    > Agree. Will use s64 in this code. As s32 has the same issue with what we
    > have(unsigned long) on 32 bit machine today: it is not enough for ext3
    > to support more than 2**31 free blocks, and also obviously not enough
    > for 64 bit ext3 that Laurent is working on.

    I think Andrew's suggestion was to change global counter to s64 and local
    counter to s32. That way we avoid allocating a 64 bit local counter on 64
    bit systems when we could do with a 32 bit counter. (although there is no
    real space savings with current alloc_percpu ;), but hopefully that will
    change in the future)

    >
    > I looked at the all users of percpu counter that are currently in
    > mainline(2.6.17-rc1) and in mm tree(2.6.17-rc1-mm2), they are:
    >
    > 1. ext2 free blocks/inodes/dirs
    > (int type, to be changed to unsinged long)
    > 2. ext3 free blocks/inodes/dirs
    > (int type, changing to unsigned long or unsigned long long)
    > 3. nr_files
    > (currently int type)
    > 4. decnet_memory allocated
    > (was atomic_t type in mainline, changed to percpu counter type in mm)
    > 5. tcp_memory allocated
    > (was atomic_t type, changed to percpu counter type in mm tree)
    >
    > I could be wrong, but I think there will be no effect to change the size
    > of the global counter from "long" to s64 for above percpu counter users,
    > except gives the counter more room to grow. Kiran, what do you think?

    Agree. Since the counters were earlier int/atomic_t, s32 on local and s64 on
    global should be OK.

    > Did I miss any other users of the perpcu counters?

    No, AFAIK, these are the only users as of now.

    Thanks,
    Kiran
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