On Wed, Apr 01, 2015 at 07:34:27PM -0700, Darrick J. Wong wrote: > e2fsck pass1 is modified to use the block group data prefetch function > to try to fetch the inode tables into the pagecache before it is > needed. We iterate through the blockgroups until we have enough inode > tables that need reading such that we can issue readahead; then we sit > and wait until the last inode table block read of the last group to > start fetching the next bunch. > > pass2 is modified to use the dirblock prefetching function to prefetch > the list of directory blocks that are assembled in pass1. We use the > "iterate a subset of a dblist" and avoid copying the dblist. Directory > blocks are fetched incrementally as we walk through the directory > block list. In previous iterations of this patch we would free the > directory blocks after processing, but the performance hit to e2fsck > itself wasn't worth it. Furthermore, it is anticipated that most > users will then mount the FS and start using the directories, so they > may as well remain in the page cache. > > pass4 is modified to prefetch the block and inode bitmaps in > anticipation of pass 5, because pass4 is entirely CPU bound. > > In general, these mechanisms can decrease fsck time by 10-40%, if the > host system has sufficient memory and the storage system can provide a > lot of IOPs. Pretty much any storage system capable of handling > multiple IOs in-flight at any time will see a fairly large performance > boost. (Single-issue USB mass storage disks seem to suffer badly.) > > By default, the readahead buffer size will be set to the size of a block > group's inode table (which is 2MiB for a regular ext4 FS). The -E > readahead_kb= option can be given to specify the amount of memory to > use for readahead or zero to disable it entirely; or an option can be > given in e2fsck.conf. > > v2: Fix an off-by-one error in the pass1 readahead which made the > readahead trigger one inode too late if the block groups are full. > > v3: Use the dblist partial iterator function to read ahead parts > of the directory block list in pass 2, instead of making sublists. > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Thanks, applied. - Ted -- 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
