Hi Vyacheslav, On Wed, 15 Jan 2014 16:01:44 +0400, Vyacheslav Dubeyko wrote: > Hi Clemens, > > On Wed, 2014-01-15 at 12:44 +0100, Clemens Eisserer wrote: >> Hi Vyacheslav, >> >> > The main approach of NILFS2 is COW (copy-on-write) policy. It means that >> > all data and metadata are written in log manner. Only superblocks are >> > placed in fixed positions and updated there. First superblock is located >> > in the volume begin, second one in the volume end. >> >> Can you give me an estime how often the superblock is updated / written to? >> > > NILFS2 has special method nilfs_sb_need_update() [1] and special > constant NILFS_SB_FREQ [2] that it is used usually for definition > frequency of superblocks updating. So, as far as I can judge, default > value of such frequency under high I/O load is 10 seconds (Minimum > interval of periodical update of superblocks (in seconds)). > > With the best regards, > Vyacheslav Dubeyko. > > [1] http://lxr.free-electrons.com/source/fs/nilfs2/the_nilfs.h#L254 > [2] http://lxr.free-electrons.com/source/fs/nilfs2/the_nilfs.h#L252 By the way, do you have any nice idea to stop periodical update of superblocks? Most information on the superblock is static (layout information or so). sbp->s_state has an ERROR state bit and a VALID state bit, but these bits are mostly static. sbp->s_free_blocks_count keeps free block count at the time, but I think this information is not important because it can be calculated from the number of clean segments. We need to the periodical in-place superblock write only for updating a pointer to the most latest log. And, this will be eliminable if we can invent the fast way to determine the latest log. Regards, Ryusuke Konishi -- To unsubscribe from this list: send the line "unsubscribe linux-nilfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
