On Wed, May 09, 2007 at 12:06:52PM -0500, Matt Mackall wrote: > On Wed, May 09, 2007 at 12:56:39AM -0700, Valerie Henson wrote: > > On Sun, Apr 29, 2007 at 08:40:42PM -0500, Matt Mackall wrote: > > > > > > This does mean that our time to make progress on a check is bounded at > > > the top by the size of our largest file. If we have a degenerate > > > filesystem filled with a single file, this will in fact take as long > > > as a conventional fsck. If your filesystem has, say, 100 roughly > > > equally-sized files, you're back in Chunkfs territory. > > > > Hm, I'm not sure that everyone understands, a particular subtlety of > > how the fsck algorithm works in chunkfs. A lot of people seem to > > think that you need to check *all* cross-chunk links, every time an > > individual chunk is checked. That's not the case; you only need to > > check the links that go into and out of the dirty chunk. You also > > don't need to check the other parts of the file outside the chunk, > > except for perhaps reading the byte range info for each continuation > > node and making sure no two continuation inodes think they both have > > the same range, but you don't check the indirect blocks, block > > bitmaps, etc. > > My reference to chunkfs here is simply that the worst-case is checking ~1 > chunk, which is about 1/100th of a volume. I understand that being the case if each file is only in one tile. Does the fpos make this irrelevant as well? > > > So we should have no trouble checking an exabyte-sized filesystem on a > > > 4MB box. Even if it has one exabyte-sized file! We check the first > > > tile, see that it points to our file, then iterate through that file, > > > checking that the forward and reverse pointers for each block match > > > and all CRCs match, etc. We cache the file's inode as clean, finish > > > checking anything else in the first tile, then mark it clean. When we get > > > to the next tile (and the next billion after that!), we notice that > > > each block points back to our cached inode and skip rechecking it. > > > > If I understand correctly then, if you do have a one exabyte sized > > file, and any part of it is in a dirty tile, you will need to check > > the whole file? Or will Joern's fpos proposal fix this? > > Yes, the original idea is you have to check every file that "covers" a > tile in its entirety. With Joern's fpos piece, I think we can restrict > our checks to just the section of the file that covers the tile. Hrm. Can you help me understand how you would check i_size then? -VAL - 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
