[OpenAFS-devel] 2.6.16 linux and d_cache

[chas williams - CONTRACTOR]

looks like they merged these two members of the dentry.  neither
would be in use at the same time, you are either a child or on
the unused list.

i would change d_child to d_u.d_child.

In message <1140738303.2689.11.camel@billmurray.pp.rl.ac.uk>,William John Murra
y writes:
>  Hello all,
>         I am still trying to get AFS on 2.6.16 linux.
>The latest snapshots, and 1.5.0 have a new routine in afs_callback.c
>which does not compile:
>'struct dentry=E2=80=99 has no member named =E2=80=98d_child'
>
>This seems to be due to the patch at the bottom.
>
>So now we have:
>	/*
>	 * d_child and d_rcu can share memory
>	 */
>	union {
>		struct list_head d_child;	/* child of parent list */
>	 	struct rcu_head d_rcu;
>	} d_u;
>
>Does anyone know how should this be d_child be referenced?
>d_u.d_cache is wrong...
>   Thank you,
>           Bill
>
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
>=3D
>commit 5160ee6fc891a9ca114be0e90fa6655647bb64b2
>Author: Eric Dumazet <dada1@cosmosbay.com>
>Date:   Sun Jan 8 01:03:32 2006 -0800
>
>[PATCH] shrink dentry struct
>Some long time ago, dentry struct was carefully tuned so that on 32 bits
>UP, sizeof(struct dentry) was exactly 128, ie a power of 2, and a
>multiple
>of memory cache lines.
>   =20
>Then RCU was added and dentry struct enlarged by two pointers, with nice
>results for SMP, but not so good on UP, because breaking the above
>tuning
>(128 + 8 =3D 136 bytes)
>   =20
>This patch reverts this unwanted side effect, by using an union (d_u),
>where d_rcu and d_child are placed so that these two fields can share
>their memory needs.
>   =20
>At the time d_free() is called (and d_rcu is really used), d_child is
>known to be empty and not touched by the dentry freeing.
>   =20
>Lockless lookups only access d_name, d_parent, d_lock, d_op, d_flags (so
>the previous content of d_child is not needed if said dentry was
>unhashed
>but still accessed by a CPU because of RCU constraints)
>   =20
>As dentry cache easily contains millions of entries, a size reduction is
>worth the extra complexity of the ugly C union.
>
>