Bharata B Rao: > - The cache can grow arbitrarily large in size for big directories thereby > consuming lots of memory. Pruning individual cache entries is out of question > as entire cache is needed for subsequent readdirs for duplicate elimination. Additionally, the memory usage may be a problem too since your implementation calls kmalloc() for every names. > - Whenever _any_ directory that is part of the union gets > modified (addition/deletion of entries), the dirent cache of all the unions > which this directory is part of, needs to be purged and rebuilt. This is > expensive not only due to re-reads of dirents but also because > readdir(2)/getdents(2) needs to be synchronized with other operations > like mkdir/mknod/link/unlink etc. The cache in struct file doesn't need to be refreshed unless rewinddir() is issued. Also you can maintain the cache in every add/del entries, instead of discarding the cache entirely. > After all this, I am beginning to think if it would be better to delegate > this readdir and whiteout processing to userspace. Can this be better handled Yes, I had such idea once. And copy-up too. They can be done in userspace (while you need to be careful about the privilege). Anyway I agree with you. As I wrote before, this approach consumes a lot of memory and cpu (for comparing whiteouted names). Junjiro Okajima - 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
