>>> How much space does a typical file system need to encode a handle? Am I >>> right that for must it is just a few bytes? (I just glanced at the code >>> so I might be wrong.) In which case, could the handle buffer be allocated >>> dynamically depending on the underlying filesystem? Perhaps adding a >>> facility to query a filesystem about its maximum handle buffer needs? Do >>> you think the saving would justify this extra work? >> >> Well, the MAX_HANDLE_SZ is taken from NFSv4 and is 128 bytes which is quite >> big for inotify extension indeed. The good news is that this amount of bytes >> seem to be required for the most descriptive fhandle -- with info about >> parent, etc. We don't need such, we can live with shorter handle, people >> said that 40 bytes was enough for that. >> >> However, your idea about determining the handle size dynamically seems >> promising. As far as I can see from the code we can call for encode_fh with >> size equals zero and filesystem would report back the amount of bytes it >> requires for a handle. >> >> We can try going this route, what do you think? > > Sounds much better since that would only add one pointer to the watch > structure in the normal case. > > Also at checkpoint time it will use only a few bytes (compared to 64) for the > encode buffer for most filesystems. This part is probably not that important > but still a win.
No, the thing is -- we need to know the handle _before_ we start checkpoint. More exactly -- at the time the inotify_add_watch is called. So the memory save would be not that big. > Regards, > > Tvrtko Thanks, Pavel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
