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Simplify/fix dnode_move() for dn_zfetch. #11998

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May 7, 2021
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Simplify/fix dnode_move() for dn_zfetch. #11998

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8 changes: 1 addition & 7 deletions module/zfs/dnode.c
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Original file line number Diff line number Diff line change
Expand Up @@ -754,7 +754,6 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
ASSERT(!RW_LOCK_HELD(&odn->dn_struct_rwlock));
ASSERT(MUTEX_NOT_HELD(&odn->dn_mtx));
ASSERT(MUTEX_NOT_HELD(&odn->dn_dbufs_mtx));
ASSERT(!MUTEX_HELD(&odn->dn_zfetch.zf_lock));

/* Copy fields. */
ndn->dn_objset = odn->dn_objset;
Expand Down Expand Up @@ -822,19 +821,14 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
ndn->dn_newgid = odn->dn_newgid;
ndn->dn_newprojid = odn->dn_newprojid;
ndn->dn_id_flags = odn->dn_id_flags;
dmu_zfetch_init(&ndn->dn_zfetch, NULL);
list_move_tail(&ndn->dn_zfetch.zf_stream, &odn->dn_zfetch.zf_stream);
ndn->dn_zfetch.zf_dnode = odn->dn_zfetch.zf_dnode;
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Does this leak the zstream_t's on the zf_stream?

The move callbacks are pretty tricky code to get right. IMO, if we aren't able to maintain the move callbacks, because we can't test them, because they are dead code, we should remove them from the codebase.

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@amotin amotin May 5, 2021 •
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dmu_zfetch_fini(&odn->dn_zfetch) below should free the old streams gracefully. I've preferred to drop streams exactly to not complicate this code and avoid new breakages later.

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OK. I'm fine with integrating this change, but I would welcome a future PR to remove dnode_move_impl() entirely.

dmu_zfetch_init(&ndn->dn_zfetch, ndn);

/*
* Update back pointers. Updating the handle fixes the back pointer of
* every descendant dbuf as well as the bonus dbuf.
*/
ASSERT(ndn->dn_handle->dnh_dnode == odn);
ndn->dn_handle->dnh_dnode = ndn;
if (ndn->dn_zfetch.zf_dnode == odn) {
ndn->dn_zfetch.zf_dnode = ndn;
}

/*
* Invalidate the original dnode by clearing all of its back pointers.
Expand Down