On Fri, Jun 07, 2019 at 06:35:42AM +0000, Andriy Gapon wrote: > Author: avg > Date: Fri Jun 7 06:35:42 2019 > New Revision: 348772 > URL: https://svnweb.freebsd.org/changeset/base/348772 > > Log: > Restore ARC MFU/MRU pressure > > 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 <s...@zxy.spb.ru> > MFC after: 2 weeks > Sponsored by: Integros [integros.com] > Differential Revision: https://reviews.freebsd.org/D19094
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