Date: Fri, 9 Jun 2017 15:01:18 +0000 (UTC) From: Andriy Gapon <avg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-vendor@freebsd.org Subject: svn commit: r319741 - vendor-sys/illumos/dist/uts/common/fs/zfs Message-ID: <201706091501.v59F1IoC028069@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: avg Date: Fri Jun 9 15:01:18 2017 New Revision: 319741 URL: https://svnweb.freebsd.org/changeset/base/319741 Log: 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 <dan.kimmel@delphix.com> Reviewed by: Paul Dagnelie <pcd@delphix.com> Approved by: Robert Mustacchi <rm@joyent.com> Author: Matthew Ahrens <mahrens@delphix.com> Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/dbuf.c Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/dbuf.c ============================================================================== --- vendor-sys/illumos/dist/uts/common/fs/zfs/dbuf.c Fri Jun 9 15:00:13 2017 (r319740) +++ vendor-sys/illumos/dist/uts/common/fs/zfs/dbuf.c Fri Jun 9 15:01:18 2017 (r319741) @@ -561,19 +561,15 @@ 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); } }
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201706091501.v59F1IoC028069>