On Thu, Jan 25, 2018 at 12:17 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Thu, Jan 25, 2018 at 10:58 AM, Hou Tao <houtao1@xxxxxxxxxx> wrote: >> Now each whiteout file will be assigned a new inode. To reduce the >> overhead of allocating and freeing inodes in upper fs, creating a >> whiteout file under workbasedir and hardlink all whiteout files into it. >> >> The effect is obvious: under my VM, the time used for removing the >> linux kernel source tree will be reduced from 17s to 10s. >> >> Got the idea from autofs. > > Yep, this was talked about, then forgotten. Thanks for bringing it up. > > The implementation is a little more difficult though, because there's > a limit to how many hard links to a single file are allowed. > > So it should be something like: > > - try hard linking "singleton", if succeeds then fine > - else unlink old singleton from workdir, create new one and use that one (only in case link error is EMLINK) - else if error is EXDEV then upper probably has a project id different than the singleton, so fall back to no hardlink > > If it's possible to get a filesystem as upper that doesn't support > hard links at all, then that also needs to be taken care of, to fall > back to non-hard linked whiteouts. Chengguang's patch for project id already does a test link on mount, so that is a good starting point. if link fails and NOT because of EXDEV, then index also cannot be used... Thanks, Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
