lkml.org 
[lkml]   [2007]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH 3/3] have pipefs ensure i_ino uniqueness by calling iunique and hashing the inode
    Date
    On Friday 26 January 2007 15:42, Jeff Layton wrote:
    > Kirill Korotaev wrote:
    > > Jeff,
    > >
    > > is 100% uniqeness is so much required for pipe inode numbers?
    > > AFAIU, it is not that critical for pipefs (unlike smb, nfs etc.)
    > >
    > > Thanks,
    > > Kirill
    >
    > There is no in-kernel reason why i_ino uniqueness is important for
    > pipefs. Where it might matter is userspace. The i_ino value is used for:
    >
    > 1) the st_ino value returned in stat calls
    >
    > 2) the dentry name (generated as "[inode_number]")
    >
    > So while it's certainly not "correct" to have multiple inodes with the same
    > number on any filesystem, it is probably more important in some places is
    > others. For pipefs, maybe it isn't, especially given a potential 6%
    > performance impact to fix it. Anyone else have thoughts?

    For dentry name, we certainly could use "[address of inode]" instead
    of "[inode number]" to get unicity, but do we care ?

    For st_ino values on pipefs and sockets, I doubt any user application would
    care. I never had to fstat() a socket fd. Of course it's a file descriptor,
    but all we really want to do with this kind of file descriptor is to call
    socket API.

    And for some heavy loaded internet servers , the additional cost of
    insert/delete a node in a machine shared tree could be a problem.

    Some weeks ago I suggested to not hash pipe/socket dentries in order to save
    some locked ops (see commits 304e61e6fbadec586dfe002b535f169a04248e49 &
    b3423415fbc2e5461605826317da1c8dbbf21f97 ), so obviously I prefer not adding
    another tree ops. However, pipe/sockets creation/destroy are probably not
    that frequent, so the 6% perf impact is not that big :)

    Eric
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-01-26 16:15    [W:2.710 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site