Messages in this thread | | | Subject | Re: [Ext2-devel] [PATCH 2/2] ext2/3: Support2^32-1blocks(e2fsprogs) | From | Laurent Vivier <> | Date | Wed, 29 Mar 2006 11:13:26 +0200 |
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Le mar 28/03/2006 à 20:01, Mingming Cao a écrit : > On Tue, 2006-03-28 at 09:15 +0200, Laurent Vivier wrote: > > Le mar 28/03/2006 à 00:58, Ravikiran G Thirumalai a écrit : > > > On Mon, Mar 27, 2006 at 01:10:49PM -0800, Andrew Morton wrote: > > > > 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. > > > > > > 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. > > > > As 64bit per cpu counter is used only by ext3 and needed only on 64bit > > architecture and when CONFIG_LBD is set, perhaps we can have only one > > implementation, 32bit in the case of 32bit arch and 64bit in the case of > > 64bit arch + LBD, as I did in my 64bit patches for ext3 ? > > > > The current percpu counter on 32 bit machine is "long", a signed value. > It's a problem for ext3 on 32 bit arch also, as the total number of free > blocks in ext3 is a type of u32. Isn't it? Did I miss something?
You're right, Mingming.
But I think instead of thinking to change "long" by "long long" we should think about changing "long" by "unsigned long" in the per-cpu counter structure.
Is there someone knowing why this counter is signed ?
Laurent -- Laurent Vivier Bull, Architect of an Open World (TM) http://www.bullopensource.org/ext4 [unhandled content-type:application/pgp-signature] | |