[PATCH 6/8] lib/lzo: implement run-length encoding

[Dave Rodgman]

When using zram, we frequently encounter long runs of zero bytes.
This adds a special case which identifies runs of zeros and encodes
them using run-length encoding.

This is faster for both compression and decompresion. For
high-entropy data which doesn't hit this case, impact is minimal.

Compression ratio is within a few percent in all cases.

This modifies the bitstream in a way which is backwards compatible
(i.e., we can decompress old bitstreams, but old versions of lzo
cannot decompress new bitstreams).

Link: http://lkml.kernel.org/r/20181127161913.23863-7-dave.rodgman@xxxxxxx
Signed-off-by: Dave Rodgman <dave.rodgman@xxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Markus F.X.J. Oberhumer <markus@xxxxxxxxxxxxx>
Cc: Matt Sealey <matt.sealey@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nitin Gupta <nitingupta910@xxxxxxxxx>
Cc: Richard Purdie <rpurdie@xxxxxxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Sonny Rao <sonnyrao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
---
 Documentation/lzo.txt           | 35 +++++++++---
 include/linux/lzo.h             |  2 +-
 lib/lzo/lzo1x_compress.c        | 98 +++++++++++++++++++++++++++++----
 lib/lzo/lzo1x_decompress_safe.c | 75 +++++++++++++++++--------
 lib/lzo/lzodefs.h               | 12 +++-
 5 files changed, 180 insertions(+), 42 deletions(-)

diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt
index 6fa6a93d0949..306c60344ca7 100644
--- a/Documentation/lzo.txt
+++ b/Documentation/lzo.txt
@@ -78,16 +78,30 @@ Description
      is an implementation design choice independent on the algorithm or
      encoding.
 
+Versions
+
+0: Original version
+1: LZO-RLE
+
+Version 1 of LZO implements an extension to encode runs of zeros using run
+length encoding. This improves speed for data with many zeros, which is a
+common case for zram. This modifies the bitstream in a backwards compatible way
+(v1 can correctly decompress v0 compressed data, but v0 cannot read v1 data).
+
 Byte sequences
 ==============
 
   First byte encoding::
 
-      0..17   : follow regular instruction encoding, see below. It is worth
-                noting that codes 16 and 17 will represent a block copy from
-                the dictionary which is empty, and that they will always be
+      0..16   : follow regular instruction encoding, see below. It is worth
+                noting that code 16 will represent a block copy from the
+                dictionary which is empty, and that it will always be
                 invalid at this place.
 
+      17      : bitstream version. If the first byte is 17, the next byte
+                gives the bitstream version. If the first byte is not 17,
+                the bitstream version is 0.
+
       18..21  : copy 0..3 literals
                 state = (byte - 17) = 0..3  [ copy <state> literals ]
                 skip byte
@@ -140,6 +154,11 @@ Byte sequences
            state = S (copy S literals after this block)
            End of stream is reached if distance == 16384
 
+        In version 1, this instruction is also used to encode a run of zeros if
+        distance = 0xbfff, i.e. H = 1 and the D bits are all 1.
+           In this case, it is followed by a fourth byte, X.
+           run length = ((X << 3) | (0 0 0 0 0 L L L)) + 4.
+
       0 0 1 L L L L L  (32..63)
            Copy of small block within 16kB distance (preferably less than 34B)
            length = 2 + (L ?: 31 + (zero_bytes * 255) + non_zero_byte)
@@ -165,7 +184,9 @@ Authors
 =======
 
   This document was written by Willy Tarreau <w@xxxxxx> on 2014/07/19 during an
-  analysis of the decompression code available in Linux 3.16-rc5. The code is
-  tricky, it is possible that this document contains mistakes or that a few
-  corner cases were overlooked. In any case, please report any doubt, fix, or
-  proposed updates to the author(s) so that the document can be updated.
+  analysis of the decompression code available in Linux 3.16-rc5, and updated
+  by Dave Rodgman <dave.rodgman@xxxxxxx> on 2018/10/30 to introduce run-length
+  encoding. The code is tricky, it is possible that this document contains
+  mistakes or that a few corner cases were overlooked. In any case, please
+  report any doubt, fix, or proposed updates to the author(s) so that the
+  document can be updated.
diff --git a/include/linux/lzo.h b/include/linux/lzo.h
index 2ae27cb89927..547a86c71e1b 100644
--- a/include/linux/lzo.h
+++ b/include/linux/lzo.h
@@ -18,7 +18,7 @@
 #define LZO1X_1_MEM_COMPRESS	(8192 * sizeof(unsigned short))
 #define LZO1X_MEM_COMPRESS	LZO1X_1_MEM_COMPRESS
 
-#define lzo1x_worst_compress(x) ((x) + ((x) / 16) + 64 + 3)
+#define lzo1x_worst_compress(x) ((x) + ((x) / 16) + 64 + 3 + 2)
 
 /* This requires 'wrkmem' of size LZO1X_1_MEM_COMPRESS */
 int lzo1x_1_compress(const unsigned char *src, size_t src_len,
diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c
index 82fb5571ce5e..fa8d4ff38531 100644
--- a/lib/lzo/lzo1x_compress.c
+++ b/lib/lzo/lzo1x_compress.c
@@ -20,7 +20,7 @@
 static noinline size_t
 lzo1x_1_do_compress(const unsigned char *in, size_t in_len,
 		    unsigned char *out, size_t *out_len,
-		    size_t ti, void *wrkmem)
+		    size_t ti, void *wrkmem, signed char *state_offset)
 {
 	const unsigned char *ip;
 	unsigned char *op;
@@ -38,24 +38,82 @@ lzo1x_1_do_compress(const unsigned char *in, size_t in_len,
 		const unsigned char *m_pos;
 		size_t t, m_len, m_off;
 		u32 dv;
+		u32 run_length = 0;
 literal:
 		ip += 1 + ((ip - ii) >> 5);
 next:
 		if (unlikely(ip >= ip_end))
 			break;
 		dv = get_unaligned_le32(ip);
-		t = ((dv * 0x1824429d) >> (32 - D_BITS)) & D_MASK;
-		m_pos = in + dict[t];
-		dict[t] = (lzo_dict_t) (ip - in);
-		if (unlikely(dv != get_unaligned_le32(m_pos)))
-			goto literal;
+
+		if (dv == 0) {
+			const unsigned char *ir = ip + 4;
+			const unsigned char *limit = ip_end
+				< (ip + MAX_ZERO_RUN_LENGTH + 1)
+				? ip_end : ip + MAX_ZERO_RUN_LENGTH + 1;
+#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && \
+	defined(LZO_FAST_64BIT_MEMORY_ACCESS)
+			u64 dv64;
+
+			for (; (ir + 32) <= limit; ir += 32) {
+				dv64 = get_unaligned((u64 *)ir);
+				dv64 |= get_unaligned((u64 *)ir + 1);
+				dv64 |= get_unaligned((u64 *)ir + 2);
+				dv64 |= get_unaligned((u64 *)ir + 3);
+				if (dv64)
+					break;
+			}
+			for (; (ir + 8) <= limit; ir += 8) {
+				dv64 = get_unaligned((u64 *)ir);
+				if (dv64) {
+#  if defined(__LITTLE_ENDIAN)
+					ir += __builtin_ctzll(dv64) >> 3;
+#  elif defined(__BIG_ENDIAN)
+					ir += __builtin_clzll(dv64) >> 3;
+#  else
+#    error "missing endian definition"
+#  endif
+					break;
+				}
+			}
+#else
+			while ((ir < (const unsigned char *)
+					ALIGN((uintptr_t)ir, 4)) &&
+					(ir < limit) && (*ir == 0))
+				ir++;
+			for (; (ir + 4) <= limit; ir += 4) {
+				dv = *((u32 *)ir);
+				if (dv) {
+#  if defined(__LITTLE_ENDIAN)
+					ir += __builtin_ctz(dv) >> 3;
+#  elif defined(__BIG_ENDIAN)
+					ir += __builtin_clz(dv) >> 3;
+#  else
+#    error "missing endian definition"
+#  endif
+					break;
+				}
+			}
+#endif
+			while (likely(ir < limit) && unlikely(*ir == 0))
+				ir++;
+			run_length = ir - ip;
+			if (run_length > MAX_ZERO_RUN_LENGTH)
+				run_length = MAX_ZERO_RUN_LENGTH;
+		} else {
+			t = ((dv * 0x1824429d) >> (32 - D_BITS)) & D_MASK;
+			m_pos = in + dict[t];
+			dict[t] = (lzo_dict_t) (ip - in);
+			if (unlikely(dv != get_unaligned_le32(m_pos)))
+				goto literal;
+		}
 
 		ii -= ti;
 		ti = 0;
 		t = ip - ii;
 		if (t != 0) {
 			if (t <= 3) {
-				op[-2] |= t;
+				op[*state_offset] |= t;
 				COPY4(op, ii);
 				op += t;
 			} else if (t <= 16) {
@@ -86,6 +144,17 @@ lzo1x_1_do_compress(const unsigned char *in, size_t in_len,
 			}
 		}
 
+		if (unlikely(run_length)) {
+			ip += run_length;
+			run_length -= MIN_ZERO_RUN_LENGTH;
+			put_unaligned_le32((run_length << 21) | 0xfffc18
+					   | (run_length & 0x7), op);
+			op += 4;
+			run_length = 0;
+			*state_offset = -3;
+			goto finished_writing_instruction;
+		}
+
 		m_len = 4;
 		{
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) && defined(LZO_USE_CTZ64)
@@ -168,7 +237,6 @@ lzo1x_1_do_compress(const unsigned char *in, size_t in_len,
 
 		m_off = ip - m_pos;
 		ip += m_len;
-		ii = ip;
 		if (m_len <= M2_MAX_LEN && m_off <= M2_MAX_OFFSET) {
 			m_off -= 1;
 			*op++ = (((m_len - 1) << 5) | ((m_off & 7) << 2));
@@ -205,6 +273,9 @@ lzo1x_1_do_compress(const unsigned char *in, size_t in_len,
 			*op++ = (m_off << 2);
 			*op++ = (m_off >> 6);
 		}
+		*state_offset = -2;
+finished_writing_instruction:
+		ii = ip;
 		goto next;
 	}
 	*out_len = op - out;
@@ -219,6 +290,12 @@ int lzo1x_1_compress(const unsigned char *in, size_t in_len,
 	unsigned char *op = out;
 	size_t l = in_len;
 	size_t t = 0;
+	signed char state_offset = -2;
+
+	// LZO v0 will never write 17 as first byte,
+	// so this is used to version the bitstream
+	*op++ = 17;
+	*op++ = LZO_VERSION;
 
 	while (l > 20) {
 		size_t ll = l <= (M4_MAX_OFFSET + 1) ? l : (M4_MAX_OFFSET + 1);
@@ -227,7 +304,8 @@ int lzo1x_1_compress(const unsigned char *in, size_t in_len,
 			break;
 		BUILD_BUG_ON(D_SIZE * sizeof(lzo_dict_t) > LZO1X_1_MEM_COMPRESS);
 		memset(wrkmem, 0, D_SIZE * sizeof(lzo_dict_t));
-		t = lzo1x_1_do_compress(ip, ll, op, out_len, t, wrkmem);
+		t = lzo1x_1_do_compress(ip, ll, op, out_len,
+					t, wrkmem, &state_offset);
 		ip += ll;
 		op += *out_len;
 		l  -= ll;
@@ -240,7 +318,7 @@ int lzo1x_1_compress(const unsigned char *in, size_t in_len,
 		if (op == out && t <= 238) {
 			*op++ = (17 + t);
 		} else if (t <= 3) {
-			op[-2] |= t;
+			op[state_offset] |= t;
 		} else if (t <= 18) {
 			*op++ = (t - 3);
 		} else {
diff --git a/lib/lzo/lzo1x_decompress_safe.c b/lib/lzo/lzo1x_decompress_safe.c
index aa95d3066b7d..b8f88d5ea3ff 100644
--- a/lib/lzo/lzo1x_decompress_safe.c
+++ b/lib/lzo/lzo1x_decompress_safe.c
@@ -46,11 +46,23 @@ int lzo1x_decompress_safe(const unsigned char *in, size_t in_len,
 	const unsigned char * const ip_end = in + in_len;
 	unsigned char * const op_end = out + *out_len;
 
+	unsigned char bitstream_version;
+
 	op = out;
 	ip = in;
 
 	if (unlikely(in_len < 3))
 		goto input_overrun;
+
+	if (likely(*ip == 17)) {
+		bitstream_version = ip[1];
+		ip += 2;
+		if (unlikely(in_len < 5))
+			goto input_overrun;
+	} else {
+		bitstream_version = 0;
+	}
+
 	if (*ip > 17) {
 		t = *ip++ - 17;
 		if (t < 4) {
@@ -151,32 +163,49 @@ int lzo1x_decompress_safe(const unsigned char *in, size_t in_len,
 			m_pos -= next >> 2;
 			next &= 3;
 		} else {
-			m_pos = op;
-			m_pos -= (t & 8) << 11;
-			t = (t & 7) + (3 - 1);
-			if (unlikely(t == 2)) {
-				size_t offset;
-				const unsigned char *ip_last = ip;
+			NEED_IP(2);
+			next = get_unaligned_le16(ip);
+			if (((next & 0xfffc) == 0xfffc) &&
+			    ((t & 0xf8) == 0x18) &&
+			    likely(bitstream_version)) {
+				NEED_IP(3);
+				t &= 7;
+				t |= ip[2] << 3;
+				t += MIN_ZERO_RUN_LENGTH;
+				NEED_OP(t);
+				memset(op, 0, t);
+				op += t;
+				next &= 3;
+				ip += 3;
+				goto match_next;
+			} else {
+				m_pos = op;
+				m_pos -= (t & 8) << 11;
+				t = (t & 7) + (3 - 1);
+				if (unlikely(t == 2)) {
+					size_t offset;
+					const unsigned char *ip_last = ip;
 
-				while (unlikely(*ip == 0)) {
-					ip++;
-					NEED_IP(1);
-				}
-				offset = ip - ip_last;
-				if (unlikely(offset > MAX_255_COUNT))
-					return LZO_E_ERROR;
+					while (unlikely(*ip == 0)) {
+						ip++;
+						NEED_IP(1);
+					}
+					offset = ip - ip_last;
+					if (unlikely(offset > MAX_255_COUNT))
+						return LZO_E_ERROR;
 
-				offset = (offset << 8) - offset;
-				t += offset + 7 + *ip++;
-				NEED_IP(2);
+					offset = (offset << 8) - offset;
+					t += offset + 7 + *ip++;
+					NEED_IP(2);
+					next = get_unaligned_le16(ip);
+				}
+				ip += 2;
+				m_pos -= next >> 2;
+				next &= 3;
+				if (m_pos == op)
+					goto eof_found;
+				m_pos -= 0x4000;
 			}
-			next = get_unaligned_le16(ip);
-			ip += 2;
-			m_pos -= next >> 2;
-			next &= 3;
-			if (m_pos == op)
-				goto eof_found;
-			m_pos -= 0x4000;
 		}
 		TEST_LB(m_pos);
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
diff --git a/lib/lzo/lzodefs.h b/lib/lzo/lzodefs.h
index 06fa83a38e0a..682359058b3c 100644
--- a/lib/lzo/lzodefs.h
+++ b/lib/lzo/lzodefs.h
@@ -13,6 +13,12 @@
  */
 
 
+/* Version
+ * 0: original lzo version
+ * 1: lzo with support for RLE
+ */
+#define LZO_VERSION 1
+
 #define COPY4(dst, src)	\
 		put_unaligned(get_unaligned((const u32 *)(src)), (u32 *)(dst))
 #if defined(CONFIG_X86_64) || defined(CONFIG_ARM64)
@@ -31,6 +37,7 @@
 #elif defined(CONFIG_X86_64) || defined(CONFIG_ARM64)
 #define LZO_USE_CTZ64	1
 #define LZO_USE_CTZ32	1
+#define LZO_FAST_64BIT_MEMORY_ACCESS
 #elif defined(CONFIG_X86) || defined(CONFIG_PPC)
 #define LZO_USE_CTZ32	1
 #elif defined(CONFIG_ARM)
@@ -45,7 +52,7 @@
 #define M1_MAX_OFFSET	0x0400
 #define M2_MAX_OFFSET	0x0800
 #define M3_MAX_OFFSET	0x4000
-#define M4_MAX_OFFSET	0xbfff
+#define M4_MAX_OFFSET	0xbffe
 
 #define M1_MIN_LEN	2
 #define M1_MAX_LEN	2
@@ -61,6 +68,9 @@
 #define M3_MARKER	32
 #define M4_MARKER	16
 
+#define MIN_ZERO_RUN_LENGTH	4
+#define MAX_ZERO_RUN_LENGTH	(2047 + MIN_ZERO_RUN_LENGTH)
+
 #define lzo_dict_t      unsigned short
 #define D_BITS		13
 #define D_SIZE		(1u << D_BITS)
-- 
2.17.1