On Thu, Dec 9, 2010 at 6:45 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Thu, Dec 09, 2010 at 05:16:44PM +1100, Nick Piggin wrote: >> On Thu, Dec 09, 2010 at 04:43:43PM +1100, Dave Chinner wrote: >> > On Mon, Nov 29, 2010 at 09:57:33PM +1100, Nick Piggin wrote: >> > > Hey, >> > > >> > > What was the reason behind not using my approach to use fast per-cpu >> > > counters for inode and dentry counters, and instead using the >> > > percpu_counter lib (which is not useful unless very fast approximate >> > > access to the global counter is required, or performance is not >> > > critical, which is somewhat of an oxymoron if you're using per-counters >> > > in the first place). It is a difference between this: >> > >> > Hi Nick - sorry for being slow to answer this - I only just found >> > this email. >> > >> > The reason for using the generic counters is because the shrinkers >> > read the current value of the global counter on every call and hence >> > they can be read thousands of times a second. The only way to do that >> > efficiently is to use the approximately value the generic counters >> > provide. >> >> That is not what is happening, though, so I assume that no measurements >> were done. >> >> In fact what happens now is that *both* type of counters use the crappy >> percpu counter library, and the shrinkers actually do a per-cpu loop >> over the counters to get the sum. > > More likely that the overhead was hidden in the noise on the size of > machines most people test on. No. I was referring to the decision to use the heavyweight percpu_counter code over the superior per cpu data that I was using. Also, the unrelated change to make nr_unused into per-cpu was not right, and I will revert that back to a global variable. (again, unless you have numbers) > It certainly wasn't measurable on my > 16p machine, and nobody who reviewed it at the time (Ñeveral people) > picked it up. So thanks for reviewing it - the simple fix is below. > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx > > fs: Use approximate values for number of inodes and dentries > > From: Dave Chinner <dchinner@xxxxxxxxxx> Nack. Can you please address my points and actually explain why this is better than my proposed approach please? -- 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
