On Mon, Mar 27, 2006 at 01:10:49PM -0800, Andrew Morton wrote:
> Mingming Cao <[email protected]> wrote:
> >
> > I am wondering if we have (or plan to have) "long long " type of percpu
> > counters? Andrew, Kiran, do you know?
> >
> > It seems right now the percpu counters are used mostly by ext2/3 for
> > filesystem free blocks accounting. Right now the counter is "long" type,
> > which is not enough if we want to extend the filesystem limit from 2**31
> > to 2**32 on 32 bit machine.
> >
> > The patch from Takashi copies the whole percpu_count.h and create a new
> > percpu_llcounter.h to support longlong type percpu counters. I am
> > wondering is there any better way for this?
> >
>
> I can't immediately think of anything smarter.
>
> One could of course implement a 64-bit percpu counter by simply
> concatenating two 32-bit counters. That would be a little less efficient,
> but would introduce less source code and would mean that we don't need to
> keep two different implemetations in sync. But one would need to do a bit
> of implementation, see how bad it looks.
Since long long is 64 bits on both 32bit and 64 bit arches, we can just
change percpu_counter type to long long (or s64) and just have one
implementation of percpu_counter?
But reads and writes on 64 bit counters may not be atomic on all 32 bit arches.
So the implementation might have to be reviewed for that.
Thanks,
Kiran
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