On Fri, 06 Jul 2012 09:31:07 +1000 Andrew Bartlett <abartlet@xxxxxxxxx> wrote: > On Thu, 2012-07-05 at 07:24 -0400, Jeff Layton wrote: > > On Thu, 05 Jul 2012 20:02:47 +1000 > > Andrew Bartlett <abartlet@xxxxxxxxx> wrote: > > > > > (CCing in the original reporter) > > > > > > On Thu, 2012-07-05 at 18:38 +1000, Andrew Bartlett wrote: > > > > When we do a readdir() in CIFS, we are potentially efficiently > > > > collecting a great deal of current, catchable stat information. > > > > > > > > It is important that we always keep the dentry cache current for two > > > > reasons: > > > > - the information may have changed (within the actime timeout). > > > > - if we still have a dentry cache value after that timeout, it is quite > > > > expensive (1xRTT per entry) to find out if it was still correct. > > > > > > > > This hits folks who are using CIFS over a WAN very badly. For example > > > > on an emulated 50ms delay I would have ls --color complete in .1 > > > > seconds, and a second run take 4.5 seconds, as each stat() (for the > > > > colouring) would create a trans2 query_path_info query for each file, > > > > right after getting the same information in the trans2 find_first2. > > > > > > > > This patch implements the simplest approach, I would welcome a > > > > correction on if there is a better approach than d_drop() and dput(). > > > > > > > > Tested on 3.4.4-3.cifsrevalidate.fc17.i686 with a 50ms WANem emulated > > > > WAN against Samba 4.0 beta3. > > > > > > > > Thanks, > > > > > > > > Andrew Bartlett > > > > > > > Nice work tracking that down and coding up the patch. While it's not > > incorrect to drop the dentry here, we can be a little more efficient > > here and just update the inode in place if the uniqueid didn't change. > > > > Something like this (untested) patch should do it. Could you test this > > and let me know if it also helps? > > Is it really safe to update so much without getting a lock over all the > updates? > What's your worry, specifically? The vfs only requires that you hold the lock over i_size updates. I suppose it's possible that you could have racing updates to an inode, but in practice, the last one will generally "win". -- Jeff Layton <jlayton@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
