On Wed, 2006-03-29 at 17:54 -0800, Andrew Morton wrote: > Mingming Cao <cmm@xxxxxxxxxx> 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? > Hmm... I think we had this issue already even with today's 2**31 ext3. Since ext2/3 always use percpu_counter_read_positive() to get the total number of free blocks, so if the real free blocks is 0x0fff_feee, and the approximate value from the percpu counter is 0xf000_0123, the percpu_counter_read_positive() will return back 0x0000123. > 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. Sounds like the simple solution so far. Mingming - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
