svn commit: r322238 - vendor-sys/illumos/dist/uts/common/fs/zfs

[Andriy Gapon]

Author: avg
Date: Tue Aug  8 11:15:36 2017
New Revision: 322238
URL: https://svnweb.freebsd.org/changeset/base/322238

Log:
  7915 checks in l2arc_evict could use some cleaning up
  
  illumos/illumos-gate at 267ae6c3a88d2fc39276af66caafa978b0935b82
  https://github.com/illumos/illumos-gate/commit/267ae6c3a88d2fc39276af66caafa978b0935b82
  
  https://www.illumos.org/issues/7915
    l2arc_evict() is strictly serialized with respect to l2arc_write_buffers() and
    l2arc_write_done().
    Normally, l2arc_evict() and l2arc_write_buffers() are called from the same
    thread, so they can not be concurrent.
    Also, l2arc_write_buffers() uses zio_wait() on the parent zio of all cache zio-
    s.
    That ensures that l2arc_write_done() is completed before l2arc_write_buffers()
    returns.
    Finally, if a cache device is removed, then l2arc_evict() is called under
    SCL_ALL in the exclusive mode.
    That ensures that it can not be concurrent with the normal L2ARC accesses to
    the device (including writing and evicting buffers).
    Given the above, some checks and actions in l2arc_evict() do not make sense.
    For instance, it must never encounter the write head header let alone remove it
    from the buffer list.
  
  Reviewed by: Dan Kimmel <dan.kimmel at delphix.com>
  Reviewed by: Prakash Surya <prakash.surya at delphix.com>
  Approved by: Matthew Ahrens <mahrens at delphix.com>
  Author: Andriy Gapon <avg at FreeBSD.org>

Modified:
  vendor-sys/illumos/dist/uts/common/fs/zfs/arc.c

Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/arc.c
==============================================================================
--- vendor-sys/illumos/dist/uts/common/fs/zfs/arc.c	Tue Aug  8 11:14:40 2017	(r322237)
+++ vendor-sys/illumos/dist/uts/common/fs/zfs/arc.c	Tue Aug  8 11:15:36 2017	(r322238)
@@ -6755,18 +6755,16 @@ top:
 			goto top;
 		}
 
-		if (HDR_L2_WRITE_HEAD(hdr)) {
-			/*
-			 * We hit a write head node.  Leave it for
-			 * l2arc_write_done().
-			 */
-			list_remove(buflist, hdr);
-			mutex_exit(hash_lock);
-			continue;
-		}
+		/*
+		 * A header can't be on this list if it doesn't have L2 header.
+		 */
+		ASSERT(HDR_HAS_L2HDR(hdr));
 
-		if (!all && HDR_HAS_L2HDR(hdr) &&
-		    (hdr->b_l2hdr.b_daddr > taddr ||
+		/* Ensure this header has finished being written. */
+		ASSERT(!HDR_L2_WRITING(hdr));
+		ASSERT(!HDR_L2_WRITE_HEAD(hdr));
+
+		if (!all && (hdr->b_l2hdr.b_daddr >= taddr ||
 		    hdr->b_l2hdr.b_daddr < dev->l2ad_hand)) {
 			/*
 			 * We've evicted to the target address,
@@ -6776,7 +6774,6 @@ top:
 			break;
 		}
 
-		ASSERT(HDR_HAS_L2HDR(hdr));
 		if (!HDR_HAS_L1HDR(hdr)) {
 			ASSERT(!HDR_L2_READING(hdr));
 			/*
@@ -6798,9 +6795,6 @@ top:
 				ARCSTAT_BUMP(arcstat_l2_evict_reading);
 				arc_hdr_set_flags(hdr, ARC_FLAG_L2_EVICTED);
 			}
-
-			/* Ensure this header has finished being written */
-			ASSERT(!HDR_L2_WRITING(hdr));
 
 			arc_hdr_l2hdr_destroy(hdr);
 		}