On Tue, 2 Feb 2010, Olivier Galibert wrote: > > On Tue, Feb 02, 2010 at 10:40:41AM -0800, Linus Torvalds wrote: > > IOW, if you start off with a SEEK_END, I think it's reasonable to expect > > it to _not_ read the whole thing. > > I've seen a lot of: > int fd = open(...); > size = lseek(fd, 0, SEEK_END); > lseek(fd, 0, SEEK_SET); > > data = malloc(size); > read(fd, data, size); > close(fd); > > Why not fstat? I don't know. Well, the above will work perfectly with or without the patch, since it does the read of the full size. There is no read-ahead hint necessary for that kind of single read behavior. Rememebr: read-ahead is about filling the empty IO spaces _between_ reads, and turning many smaller reads into one bigger one. If you only have a single big read, read-ahead cannot help. Also, keep in mind that read-ahead is not always a win. It can be a huge loss too. Which is why we have _heuristics_. They fundamentally cannot catch every case, but what they aim for is to do a good job on average. Linus -- 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
