Re: [RFC PATCH 0/5] Union Mount: A Directory listing approach with lseek support

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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

[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux