Before r305323 (MFV r302991: 6950 ARC should cache compressed data)
arc_read() code did this for access to a ghost buffer:
arc_adapt() (from arc_get_data_buf())
arc_access(hdr, hash_lock)
I.e., we first checked access to the MFU ghost/MRU ghost buffer and
adapt MFU/MRU sizes (in arc_adapt()) and next move buffer from the ghost
state to regular.
After r305323 the sequence is different:
arc_access(hdr, hash_lock);
arc_hdr_alloc_pabd(hdr);
I.e., we first move the buffer from the ghost state in arc_access() and
then we check access to buffer in ghost state (in arc_hdr_alloc_pabd()
-> arc_get_data_abd() -> arc_get_data_impl() -> arc_adapt()). This is
incorrect: arc_adapt() never see access to the ghost buffer because
arc_access() already migrated the buffer from the ghost state to
regular.
So, the fix is to restore a call to arc_adapt() before arc_access() and
to suppress the call to arc_adapt() after arc_access().
Submitted by: Slawa Olhovchenkov <slw@zxy.spb.ru>
MFC after: 2 weeks
Sponsored by: Integros [integros.com]
Differential Revision: https://reviews.freebsd.org/D19094
d8b12a2162