On 04/22/2011 11:06 AM, Andreas Dilger wrote:
Sure, there are lots of wasted syscalls, but in this case the cost of doing extra SEEK_DATA and SEEK_HOLE operations may be fairly costly. This involves scanning the whole disk layout, possibly over a network, which might need tens or hundreds of disk seeks to read the metadata, unlike regular SEEK_SET. Even SEEK_END is somewhat costly on a network filesystem, since the syscall needs to lock the file size in order to determine the end of the file, which can block other threads from writing to the file. So while I agree that the Linux mantra that "syscalls are cheap" is true if those syscalls don't actually do any work, I think it also ignores the cost of what some syscalls need to do behind the scenes.
You have a point. I was just reviewing the possible patch for ocfs2 and it looks heavy. One option is to scrap SEEK_* and make another syscall llfind() with FIND_*. Or, do both. -- 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
