On Wed, Aug 14, 2013 at 10:10:07AM -0700, Dave Hansen wrote: > We talked a little about this issue in this thread: > > http://marc.info/?l=linux-mm&m=137573185419275&w=2 > > but I figured I'd follow up with a full comparison. ext4 is about 20% > slower in handling write page faults than ext3. Let's take a step back from the details of whether the benchmark is measuring what it claims to be measuring, and address this a different way --- what's the workload which might be run on an 8-socket, 80-core system, which is heavily modifying mmap'ed pages in such a way that all or most of the memory writes are to clean pages that require write page fault handling? We can talk about isolating the test so that we remove block allocation, timestamp modifications, etc., but then are we stil measuring whatever motivated Dave's work in the first place? IOW, if it really is about write page fault handling, the simplest test to do is to mmap /dev/zero and then start dirtying pages. At that point we will be measuring the VM level write page fault code. If we start trying to add in file system specific behavior, then we get into questions about block allocation vs. inode updates vs. writeback code paths, depending on what we are trying to measure, which then leads to the next logical question --- why are we trying to measure this? Is there a specific scalability problem that is show up in some real world use case? Or is this a theoretical exercise? It's Ok if it's just theoretical, since then we can try to figure out some kind of useful scalability limitation which is of practical importance. But if there was some original workload which was motivating this exercise, it would be good if we kept this in mind.... Cheers, - Ted -- 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
