Re: [Ext2-devel] [PATCH 2/2] ext2/3: Support2^32-1blocks(e2fsprogs)

[Andrew Morton <akpm@osdl.org>]

Mingming Cao <cmm@us.ibm.com> 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.
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