svn commit: r274628 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Andriy Gapon]

Author: avg
Date: Mon Nov 17 14:45:42 2014
New Revision: 274628
URL: https://svnweb.freebsd.org/changeset/base/274628

Log:
  l2arc: restore correct rounding up of asize of compressed data
  
  This rounding up was lost in a mismerge of illumos code.
  See r268075 MFV r267565.
  After that commit zio_compress_data() no longer performs any compressed
  size adjustment, so it needs to be done externally.  On FreeBSD we round
  up the size using vdev_ashift rather than SPA_MINBLOCKSIZE so that 4KB
  devices are properly supported.
  
  Additionally, zero out the buffer tail only if compression succeeds.
  The compression is considered successful if the size of compressed
  data after rounding up to account for the vdev ashift is less than the
  original data size.  It does not make sense to have the data compressed
  if all the savings are lost to rounding up.
  With the new zio_compress_data() it could have been possible that the
  rounded compressed size would be greater than the original size and thus
  we could zero beyond the allocated buffer if the zeroing code was kept
  at the original place.
  
  Discussed with:	delphij, gibbs
  MFC after:	2 weeks
  X-MFC with:	r274627

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Mon Nov 17 14:16:02 2014	(r274627)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c	Mon Nov 17 14:45:42 2014	(r274628)
@@ -5326,12 +5326,6 @@ l2arc_compress_buf(l2arc_buf_hdr_t *l2hd
 	csize = zio_compress_data(ZIO_COMPRESS_LZ4, l2hdr->b_tmp_cdata,
 	    cdata, l2hdr->b_asize);
 
-	rounded = P2ROUNDUP(csize, (size_t)SPA_MINBLOCKSIZE);
-	if (rounded > csize) {
-		bzero((char *)cdata + csize, rounded - csize);
-		csize = rounded;
-	}
-
 	if (csize == 0) {
 		/* zero block, indicate that there's nothing to write */
 		zio_data_buf_free(cdata, len);
@@ -5340,11 +5334,19 @@ l2arc_compress_buf(l2arc_buf_hdr_t *l2hd
 		l2hdr->b_tmp_cdata = NULL;
 		ARCSTAT_BUMP(arcstat_l2_compress_zeros);
 		return (B_TRUE);
-	} else if (csize > 0 && csize < len) {
+	}
+
+	rounded = P2ROUNDUP(csize,
+	    (size_t)1 << l2hdr->b_dev->l2ad_vdev->vdev_ashift);
+	if (rounded < len) {
 		/*
 		 * Compression succeeded, we'll keep the cdata around for
 		 * writing and release it afterwards.
 		 */
+		if (rounded > csize) {
+			bzero((char *)cdata + csize, rounded - csize);
+			csize = rounded;
+		}
 		l2hdr->b_compress = ZIO_COMPRESS_LZ4;
 		l2hdr->b_asize = csize;
 		l2hdr->b_tmp_cdata = cdata;