zio_compress: introduce max size threshold

Now default compression is lz4, which can stop compression process by itself on incompressible data. If there are additional size checks - we will only make our compressratio worse. New usable compression thresholds are: - less than BPE_PAYLOAD_SIZE (embedded_data feature); - at least one saved sector. Old 12.5% threshold is left to minimize affect on existing user expectations of CPU utilization. If data wasn't compressed - it will be saved as ZIO_COMPRESS_OFF, so if we really need to recompress data without ashift info and check anything - we can just compress it with zero threshold. So, we don't need a new feature flag here! Signed-off-by: George Melikov <[email protected]>
openzfs · May 29, 2024 · 4e64279 · 4e64279
1 parent 5137c13
commit 4e64279
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Showing 7 changed files with 54 additions and 27 deletions.
diff --git a/include/sys/zio.h b/include/sys/zio.h
@@ -29,6 +29,7 @@
  * Copyright (c) 2019, Allan Jude
  * Copyright (c) 2019, 2023, 2024, Klara Inc.
  * Copyright (c) 2019-2020, Michael Niewöhner
+ * Copyright (c) 2024 by George Melikov. All rights reserved.
  */
 
 #ifndef _ZIO_H
@@ -597,6 +598,8 @@ extern int zio_alloc_zil(spa_t *spa, objset_t *os, uint64_t txg,
 extern void zio_flush(zio_t *zio, vdev_t *vd);
 extern void zio_shrink(zio_t *zio, uint64_t size);
 
+extern size_t zio_get_compression_max_size(uint64_t gcd_alloc,
+    uint64_t min_alloc, size_t s_len);
 extern int zio_wait(zio_t *zio);
 extern void zio_nowait(zio_t *zio);
 extern void zio_execute(void *zio);

diff --git a/include/sys/zio_compress.h b/include/sys/zio_compress.h
@@ -25,6 +25,7 @@
  * Copyright (c) 2019, Klara Inc.
  * Use is subject to license terms.
  * Copyright (c) 2015, 2016 by Delphix. All rights reserved.
+ * Copyright (c) 2021, 2024 by George Melikov. All rights reserved.
  */
 
 #ifndef _SYS_ZIO_COMPRESS_H
@@ -184,7 +185,7 @@ extern int lz4_decompress_zfs(void *src, void *dst, size_t s_len, size_t d_len,
  * Compress and decompress data if necessary.
  */
 extern size_t zio_compress_data(enum zio_compress c, abd_t *src, void **dst,
-    size_t s_len, uint8_t level);
+    size_t s_len, size_t d_len, uint8_t level);
 extern int zio_decompress_data(enum zio_compress c, abd_t *src, void *dst,
     size_t s_len, size_t d_len, uint8_t *level);
 extern int zio_decompress_data_buf(enum zio_compress c, void *src, void *dst,

diff --git a/man/man7/zfsprops.7 b/man/man7/zfsprops.7
@@ -917,14 +917,24 @@ zeroes (the NUL byte).
 When a zero-filled block is detected, it is stored as
 a hole and not compressed using the indicated compression algorithm.
 .Pp
-Any block being compressed must be no larger than 7/8 of its original size
-after compression, otherwise the compression will not be considered worthwhile
-and the block saved uncompressed.
-Note that when the logical block is less than
-8 times the disk sector size this effectively reduces the necessary compression
-ratio; for example, 8 KiB blocks on disks with 4 KiB disk sectors must compress
-to 1/2
-or less of their original size.
+All blocks are allocated as a whole number of sectors
+.Pq chunks of 2^ Ns Sy ashift No bytes , e.g . Sy 512B No or Sy 4KB .
+Compression may result in a non-sector-aligned size, which will be rounded up
+to a whole number of sectors.
+If compression saves less than one whole sector,
+the block will be stored uncompressed.
+Therefore, blocks whose logical size is a small number of sectors will
+experience less compression
+(e.g. for
+.Sy recordsize Ns = Ns Sy 16K
+with
+.Sy 4K
+sectors, which have 4 sectors per block,
+compression needs to save at least 25% to actually save space on disk).
+.Pp
+There is
+.Sy 12.5%
+default compression threshold in addition to sector rounding.
 .It Xo
 .Sy context Ns = Ns Sy none Ns | Ns
 .Ar SELinux-User : Ns Ar SELinux-Role : Ns Ar SELinux-Type : Ns Ar Sensitivity-Level

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
@@ -29,6 +29,7 @@
  * Copyright (c) 2019, Klara Inc.
  * Copyright (c) 2019, Allan Jude
  * Copyright (c) 2020, The FreeBSD Foundation [1]
+ * Copyright (c) 2021, 2024 by George Melikov. All rights reserved.
  *
  * [1] Portions of this software were developed by Allan Jude
  *     under sponsorship from the FreeBSD Foundation.
@@ -1786,7 +1787,8 @@ arc_hdr_authenticate(arc_buf_hdr_t *hdr, spa_t *spa, uint64_t dsobj)
 	    !HDR_COMPRESSION_ENABLED(hdr)) {
 
 		csize = zio_compress_data(HDR_GET_COMPRESS(hdr),
-		    hdr->b_l1hdr.b_pabd, &tmpbuf, lsize, hdr->b_complevel);
+		    hdr->b_l1hdr.b_pabd, &tmpbuf, lsize, lsize,
+		    hdr->b_complevel);
 		ASSERT3P(tmpbuf, !=, NULL);
 		ASSERT3U(csize, <=, psize);
 		abd = abd_get_from_buf(tmpbuf, lsize);
@@ -8944,7 +8946,7 @@ l2arc_apply_transforms(spa_t *spa, arc_buf_hdr_t *hdr, uint64_t asize,
 		size_t bufsize = MAX(size, asize);
 		void *buf = zio_buf_alloc(bufsize);
 		uint64_t csize = zio_compress_data(compress, to_write, &buf,
-		    size, hdr->b_complevel);
+		    size, size, hdr->b_complevel);
 		if (csize > psize) {
 			/*
 			 * We can't re-compress the block into the original
@@ -10429,9 +10431,11 @@ l2arc_log_blk_commit(l2arc_dev_t *dev, zio_t *pio, l2arc_write_callback_t *cb)
 	 */
 	list_insert_tail(&cb->l2wcb_abd_list, abd_buf);
 
-	/* try to compress the buffer */
+	/* try to compress the buffer, at least one sector to save */
 	psize = zio_compress_data(ZIO_COMPRESS_LZ4,
-	    abd_buf->abd, (void **) &tmpbuf, sizeof (*lb), 0);
+	    abd_buf->abd, (void **) &tmpbuf, sizeof (*lb),
+	    zio_get_compression_max_size(dev->l2ad_vdev->vdev_ashift,
+	    dev->l2ad_vdev->vdev_ashift, sizeof (*lb)), 0);
 
 	/* a log block is never entirely zero */
 	ASSERT(psize != 0);

diff --git a/module/zfs/dmu_recv.c b/module/zfs/dmu_recv.c
@@ -1409,7 +1409,7 @@ do_corrective_recv(struct receive_writer_arg *rwa, struct drr_write *drrw,
 		    B_FALSE);
 		void *buf = abd_to_buf(cabd);
 		uint64_t csize = zio_compress_data(BP_GET_COMPRESS(bp),
-		    abd, &buf, abd_get_size(abd),
+		    abd, &buf, abd_get_size(abd), abd_get_size(abd),
 		    rwa->os->os_complevel);
 		abd_zero_off(cabd, csize, BP_GET_PSIZE(bp) - csize);
 		/* Swap in newly compressed data into the abd */

diff --git a/module/zfs/zio.c b/module/zfs/zio.c
@@ -26,6 +26,7 @@
  * Copyright (c) 2019, 2023, 2024, Klara Inc.
  * Copyright (c) 2019, Allan Jude
  * Copyright (c) 2021, Datto, Inc.
+ * Copyright (c) 2021, 2024 by George Melikov. All rights reserved.
  */
 
 #include <sys/sysmacros.h>
@@ -1675,6 +1676,21 @@ zio_roundup_alloc_size(spa_t *spa, uint64_t size)
 	return (spa->spa_min_alloc);
 }
 
+size_t
+zio_get_compression_max_size(uint64_t gcd_alloc, uint64_t min_alloc,
+    size_t s_len)
+{
+	size_t d_len;
+
+	/* minimum 12.5% must be saved (legacy value, may be changed later) */
+	d_len = s_len - (s_len >> 3);
+
+	d_len = d_len - d_len % gcd_alloc;
+	if (d_len < min_alloc)
+		return (BPE_PAYLOAD_SIZE);
+	return (d_len);
+}
+
 /*
  * ==========================================================================
  * Prepare to read and write logical blocks
@@ -1851,7 +1867,8 @@ zio_write_compress(zio_t *zio)
 	    !(zio->io_flags & ZIO_FLAG_RAW_COMPRESS)) {
 		void *cbuf = NULL;
 		psize = zio_compress_data(compress, zio->io_abd, &cbuf, lsize,
-		    zp->zp_complevel);
+		    zio_get_compression_max_size(spa->spa_gcd_alloc,
+		    spa->spa_min_alloc, lsize), zp->zp_complevel);
 		if (psize == 0) {
 			compress = ZIO_COMPRESS_OFF;
 		} else if (psize >= lsize) {
@@ -1916,7 +1933,7 @@ zio_write_compress(zio_t *zio)
 		 * to a hole.
 		 */
 		psize = zio_compress_data(ZIO_COMPRESS_EMPTY,
-		    zio->io_abd, NULL, lsize, zp->zp_complevel);
+		    zio->io_abd, NULL, lsize, lsize, zp->zp_complevel);
 		if (psize == 0 || psize >= lsize)
 			compress = ZIO_COMPRESS_OFF;
 	} else if (zio->io_flags & ZIO_FLAG_RAW_COMPRESS &&

diff --git a/module/zfs/zio_compress.c b/module/zfs/zio_compress.c
@@ -22,15 +22,11 @@
 /*
  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
- */
-/*
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
- */
-
-/*
  * Copyright (c) 2013, 2018 by Delphix. All rights reserved.
  * Copyright (c) 2019, Klara Inc.
  * Copyright (c) 2019, Allan Jude
+ * Copyright (c) 2021, 2024 by George Melikov. All rights reserved.
  */
 
 #include <sys/zfs_context.h>
@@ -126,9 +122,9 @@ zio_compress_zeroed_cb(void *data, size_t len, void *private)
 
 size_t
 zio_compress_data(enum zio_compress c, abd_t *src, void **dst, size_t s_len,
-    uint8_t level)
+    size_t d_len, uint8_t level)
 {
-	size_t c_len, d_len;
+	size_t c_len;
 	uint8_t complevel;
 	zio_compress_info_t *ci = &zio_compress_table[c];
 
@@ -145,9 +141,6 @@ zio_compress_data(enum zio_compress c, abd_t *src, void **dst, size_t s_len,
 	if (c == ZIO_COMPRESS_EMPTY)
 		return (s_len);
 
-	/* Compress at least 12.5% */
-	d_len = s_len - (s_len >> 3);
-
 	complevel = ci->ci_level;
 
 	if (c == ZIO_COMPRESS_ZSTD) {
@@ -174,7 +167,6 @@ zio_compress_data(enum zio_compress c, abd_t *src, void **dst, size_t s_len,
 	if (c_len > d_len)
 		return (s_len);
 
-	ASSERT3U(c_len, <=, d_len);
 	return (c_len);
 }