Author: avg Date: Fri Jun 9 15:28:57 2017 New Revision: 319750 URL: https://svnweb.freebsd.org/changeset/base/319750
Log: MFV r319741: 8156 dbuf_evict_notify() does not need dbuf_evict_lock illumos/illumos-gate@dbfd9f930004c390a2ce2cf850c71b4f880eef9c https://github.com/illumos/illumos-gate/commit/dbfd9f930004c390a2ce2cf850c71b4f880eef9c https://www.illumos.org/issues/8156 dbuf_evict_notify() holds the dbuf_evict_lock while checking if it should do the eviction itself (because the evict thread is not able to keep up). This can result in massive lock contention. It isn't necessary to hold the lock, because if we make the wrong choice occasionally, nothing bad will happen. Reviewed by: Dan Kimmel <[email protected]> Reviewed by: Paul Dagnelie <[email protected]> Approved by: Robert Mustacchi <[email protected]> Author: Matthew Ahrens <[email protected]> MFC after: 1 week Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c Directory Properties: head/sys/cddl/contrib/opensolaris/ (props changed) Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c ============================================================================== --- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c Fri Jun 9 15:27:22 2017 (r319749) +++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dbuf.c Fri Jun 9 15:28:57 2017 (r319750) @@ -560,19 +560,15 @@ dbuf_evict_notify(void) if (tsd_get(zfs_dbuf_evict_key) != NULL) return; + /* + * We check if we should evict without holding the dbuf_evict_lock, + * because it's OK to occasionally make the wrong decision here, + * and grabbing the lock results in massive lock contention. + */ if (refcount_count(&dbuf_cache_size) > dbuf_cache_max_bytes) { - boolean_t evict_now = B_FALSE; - - mutex_enter(&dbuf_evict_lock); - if (refcount_count(&dbuf_cache_size) > dbuf_cache_max_bytes) { - evict_now = dbuf_cache_above_hiwater(); - cv_signal(&dbuf_evict_cv); - } - mutex_exit(&dbuf_evict_lock); - - if (evict_now) { + if (dbuf_cache_above_hiwater()) dbuf_evict_one(); - } + cv_signal(&dbuf_evict_cv); } } _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "[email protected]"
