On Wed, Sep 03, 2014 at 11:52:25AM -0400, Bob Peterson wrote: > Hi, > > I sent this patch a few weeks back and it didn't receive any comments. > So I assume it's okay to add upstream? > > The problem: > If you do a fiemap operation on a very large sparse file, it can take > an extremely long amount of time (we're talking days here) because > function __generic_block_fiemap does a block-for-block search when it > encounters a hole. > > The solution: > Allow the underlying file system to return the hole size so that function > __generic_block_fiemap can quickly skip the hole. > > Preamble: > In cases where the fs-specific block_map() function finds a hole, it > can return the hole size in b_size. This is efficient because the file > system doesn't need to figure out block mapping a second time to > determine the hole size. The patch repurposes the buffer_meta flag > to tell when the fs-specific block_map() is passing back the hole_size: > If the fs-specific block_map() doesn't set the buffer_meta bit, Use of BH_Meta is a bit wierd. Mapping the data blocks of a file and expecting the return to have the BH_Meta flag set seems, well, A Little Bit Wrong. We're not short of buffer flags, perhaps adding a purpose sepcific flag for this? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
