Jerry James wrote: > On Mon, Apr 27, 2009 at 2:19 PM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote: >> Basically anything that is filled in over time, or filled in sparsely, >> could potentially benefit. > > I think the word "sparsely" here is confusing me. This function > preallocates disk space, right? So I wouldn't want to use it for a > file that I expect to be a "sparse file" throughout most or all of its > lifetime, because then I would be forcing zero-filled blocks onto the > disk. Can you explain what you meant by "filled in sparsely"? Right. Sorry, that wasn't very specific. Think of how a torrent file fills itself in: 1. [a block here]... 2. [a block there]... 3. [a little here]... ... etc and then you end up with [a block here][hole][a little here][hole][a block there].... and since the file has holes as it is being completed, I called it "sparse" Allocators often have a hard time with this kind of behavior, and telling the fs that you actually want all those blocks allocated right up front can help get a decent layout. If you are expecting your file to stay sparse, and you never really plan to fill it in, then no you probably would not want to preallocate all that space. (Just to be clear, by calling the fallocate(); call you don't actually get "zero-filled blocks on the disk" - you get quickly-allocated blocks which are marked as uninitialized, for which the filesystem will return 0s until they've been written to.) -Eric -- fedora-devel-list mailing list fedora-devel-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/fedora-devel-list
