On 06/27/13 01:04, Dave Chinner wrote:
From: Dave Chinner<dchinner@xxxxxxxxxx> During review of the separate project quota inode patches, it bcame obvious that the dquot log reservation calculation underestimated the number dquots that can be modified in a transaction. This has it's roots way back in the Irix quota implementation. That is, when quotas were first implemented in XFS, it only supported user and project quotas as Irix did not have group quotas. Hence the worst case operation involving dquot modification was calculated to involve 2 user dquots and 1 project dquot or 1 user dequot and 2 project dquots. i.e. 3 dquots. This was determined back in 1996, and has remained unchanged ever since. However, back in 2001, the Linux XFS port dropped all support for project quota and implmented group quotas over the top. This was effectively done with a search-and-replace of project with group, and as such the log reservation was not changed. However, with the advent of group quotas, chmod and rename now could modify more than 3 dquots in a single transaction - both could modify 4 dquots. Hence this log reservation has been wrong for a long time. In 2005, project quotas were reintroduced into Linux, but they were implemented to be mutually exclusive to group quotas, and so this didn't add any new changes to the dquot log reservation. hence when project quotas were in use, everything was still fine, just like in the Irix days. Now, with the addition of the separate project quota inode, group and project quotas are no longer mutually exclusive, and hence operations can now modify three dquots per inode where previously it was only two. The worst case here is the rename transaction, which can allocate/free space on two different directory inodes, and if they have different uid/gid/prid configurations and are world writeable, then rename can actually modify 6 different dquots now. Further, the dquot log reservation doesn't take into account the space used by the dquot log format structure that preceeds the dquot that is logged, and hence further underestimates the worst case log space required by dquots during a transaction. Hence the worst case log reservation needs to be increased from 3 to 6, and it needs to take into account a log format header for each of those dquots. Signed-off-by: Dave Chinner<dchinner@xxxxxxxxxx> ---
Looks good. Reviewed-by: Mark Tinguely <tinguely@xxxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
