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. xfs is about 30% slower than ext3. I'm running on an 8-socket / 80-core / 160-thread system. Test case is this: https://github.com/antonblanchard/will-it-scale/blob/master/tests/page_fault3.c It's a little easier to look at the trends as you grow the number of processes: http://www.sr71.net/~dave/intel/page-fault-exts/cmp.html?1=ext3&2=ext4&3=xfs&hide=linear,threads,threads_idle,processes_idle&rollPeriod=16 I recorded and diff'd some perf data (I've still got the raw data if anyone wants it), and the main culprit of the ext4/xfs delta looks to be spinlock contention (or at least bouncing) in xfs_log_commit_cil(). This looks to be a known problem: http://oss.sgi.com/archives/xfs/2013-07/msg00110.html Here's a brief snippet of the ext4->xfs 'perf diff'. Note that things like page_fault() go down in the profile because we are doing _fewer_ of them, not because it got faster: > # Baseline Delta Shared Object Symbol > # ........ ....... ..................... .............................................. > # > 22.04% -4.07% [kernel.kallsyms] [k] page_fault > 2.93% +12.49% [kernel.kallsyms] [k] _raw_spin_lock > 8.21% -0.58% page_fault3_processes [.] testcase > 4.87% -0.34% [kernel.kallsyms] [k] __set_page_dirty_buffers > 4.07% -0.58% [kernel.kallsyms] [k] mem_cgroup_update_page_stat > 4.10% -0.61% [kernel.kallsyms] [k] __block_write_begin > 3.69% -0.57% [kernel.kallsyms] [k] find_get_page It's a bit of a bummer that things are so much less scalable on the newer filesystems. I expected xfs to do a _lot_ better than it did. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
