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On Fri, Apr 14, 2006 at 07:51:14PM +0200, Julio M. Merino Vidal wrote:
> Hello,
>=20
> PR kern/31944 lists three issues that make tmpfs consume too much
> memory.  The attached patch addresses the first of them.  It does the
> following:
>=20
> - Only keep the node identifier/generation number when deleting a node.
>   The size of tmpfs_nid is much smaller than that of tmpfs_node.
> - Avoid keeping nodes that were initialized but then discarded due to some
>   error.  See the keepit parameter to the tmpfs_free_node function.
>=20
> I have read the replies to that PR but the proposed solutions seem to be
> "not right".  Also, one question that arises... can there be two live fil=
es in a
> file system with the same node number?  If not, all those solutions do not
> seem to address this...

As Steve noted, lots of code assumes that <dev,ino> pairs ID unique nodes.
Thus all files that stat to the same inode numbers in a given filesystem
are hardlinks to the same thing.

Thus there should not be two live, distinct files that have the same inode
#.

The only reason I see for keeping track of old generation #s is so that if=
=20
we re-use an inode #, we won't give it the same generation # again.

But the thing about generation #s is that we make them up. We export them=
=20
in file handles, and nothing is really supposed to tamper with them. :-)

So one solution is to shove 64-bit generation #s in our file handles. Then=
=20
just have one 64-bit counter we incriment each time we create a node. Add=
=20
that to someting similar to how we reuse PIDs safely, and we should be=20
set.

Take care,

Bill

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