Re: [PATCH v4] btrfs: Use larger zlib buffer for s390 hardware compression

Josef Bacik <josef@xxxxxxxxxxxxxx> · Wed, 8 Jan 2020 10:08:29 -0500

On 1/8/20 5:51 AM, Mikhail Zaslonko wrote:
In order to benefit from s390 zlib hardware compression support,
increase the btrfs zlib workspace buffer size from 1 to 4 pages (if
s390 zlib hardware support is enabled on the machine). This brings up
to 60% better performance in hardware on s390 compared to the PAGE_SIZE
buffer and much more compared to the software zlib processing in btrfs.
In case of memory pressure, fall back to a single page buffer during
workspace allocation.
The data compressed with larger input buffers will still conform to zlib
standard and thus can be decompressed also on a systems that uses only
PAGE_SIZE buffer for btrfs zlib.

Signed-off-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>


---
  fs/btrfs/compression.c |   2 +-
  fs/btrfs/zlib.c        | 135 ++++++++++++++++++++++++++++++-----------
  2 files changed, 101 insertions(+), 36 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index ee834ef7beb4..6bd0e75a822c 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1285,7 +1285,7 @@ int btrfs_decompress_buf2page(const char *buf, unsigned long buf_start,
  	/* copy bytes from the working buffer into the pages */
  	while (working_bytes > 0) {
  		bytes = min_t(unsigned long, bvec.bv_len,
-				PAGE_SIZE - buf_offset);
+				PAGE_SIZE - (buf_offset % PAGE_SIZE));
  		bytes = min(bytes, working_bytes);
  
  		kaddr = kmap_atomic(bvec.bv_page);
diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
index a6c90a003c12..05615a1099db 100644
--- a/fs/btrfs/zlib.c
+++ b/fs/btrfs/zlib.c
@@ -20,9 +20,13 @@
  #include <linux/refcount.h>
  #include "compression.h"
  
+/* workspace buffer size for s390 zlib hardware support */
+#define ZLIB_DFLTCC_BUF_SIZE    (4 * PAGE_SIZE)
+
  struct workspace {
  	z_stream strm;
  	char *buf;
+	unsigned int buf_size;
  	struct list_head list;
  	int level;
  };
@@ -61,7 +65,21 @@ struct list_head *zlib_alloc_workspace(unsigned int level)
  			zlib_inflate_workspacesize());
  	workspace->strm.workspace = kvmalloc(workspacesize, GFP_KERNEL);
  	workspace->level = level;
-	workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	workspace->buf = NULL;
+	/*
+	 * In case of s390 zlib hardware support, allocate lager workspace
+	 * buffer. If allocator fails, fall back to a single page buffer.
+	 */
+	if (zlib_deflate_dfltcc_enabled()) {
+		workspace->buf = kmalloc(ZLIB_DFLTCC_BUF_SIZE,
+					 __GFP_NOMEMALLOC | __GFP_NORETRY |
+					 __GFP_NOWARN | GFP_NOIO);
+		workspace->buf_size = ZLIB_DFLTCC_BUF_SIZE;
+	}
+	if (!workspace->buf) {
+		workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+		workspace->buf_size = PAGE_SIZE;
+	}
  	if (!workspace->strm.workspace || !workspace->buf)
  		goto fail;
  
@@ -85,6 +103,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
  	struct page *in_page = NULL;
  	struct page *out_page = NULL;
  	unsigned long bytes_left;
+	unsigned int in_buf_pages;
  	unsigned long len = *total_out;
  	unsigned long nr_dest_pages = *out_pages;
  	const unsigned long max_out = nr_dest_pages * PAGE_SIZE;
@@ -102,9 +121,6 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
  	workspace->strm.total_in = 0;
  	workspace->strm.total_out = 0;
  
-	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
-	data_in = kmap(in_page);
-
  	out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
  	if (out_page == NULL) {
  		ret = -ENOMEM;
@@ -114,12 +130,51 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
  	pages[0] = out_page;
  	nr_pages = 1;
  
-	workspace->strm.next_in = data_in;
+	workspace->strm.next_in = workspace->buf;
+	workspace->strm.avail_in = 0;
  	workspace->strm.next_out = cpage_out;
  	workspace->strm.avail_out = PAGE_SIZE;
-	workspace->strm.avail_in = min(len, PAGE_SIZE);
  
  	while (workspace->strm.total_in < len) {
+		/*
+		 * Get next input pages and copy the contents to
+		 * the workspace buffer if required.
+		 */
+		if (workspace->strm.avail_in == 0) {
+			bytes_left = len - workspace->strm.total_in;
+			in_buf_pages = min(DIV_ROUND_UP(bytes_left, PAGE_SIZE),
+					   workspace->buf_size / PAGE_SIZE);
+			if (in_buf_pages > 1) {
+				int i;
+
+				for (i = 0; i < in_buf_pages; i++) {
+					if (in_page) {
+						kunmap(in_page);
+						put_page(in_page);
+					}
+					in_page = find_get_page(mapping,
+								start >> PAGE_SHIFT);
+					data_in = kmap(in_page);
+					memcpy(workspace->buf + i * PAGE_SIZE,
+					       data_in, PAGE_SIZE);
+					start += PAGE_SIZE;
+				}
+				workspace->strm.next_in = workspace->buf;
+			} else {
+				if (in_page) {
+					kunmap(in_page);
+					put_page(in_page);
+				}
+				in_page = find_get_page(mapping,
+							start >> PAGE_SHIFT);
+				data_in = kmap(in_page);
+				start += PAGE_SIZE;
+				workspace->strm.next_in = data_in;
+			}
+			workspace->strm.avail_in = min(bytes_left,
+						       (unsigned long) workspace->buf_size);
+		}
+
  		ret = zlib_deflate(&workspace->strm, Z_SYNC_FLUSH);
  		if (ret != Z_OK) {
  			pr_debug("BTRFS: deflate in loop returned %d\n",
@@ -161,33 +216,43 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
  		/* we're all done */
  		if (workspace->strm.total_in >= len)
  			break;
-
-		/* we've read in a full page, get a new one */
-		if (workspace->strm.avail_in == 0) {
-			if (workspace->strm.total_out > max_out)
-				break;
-
-			bytes_left = len - workspace->strm.total_in;
-			kunmap(in_page);
-			put_page(in_page);
-
-			start += PAGE_SIZE;
-			in_page = find_get_page(mapping,
-						start >> PAGE_SHIFT);
-			data_in = kmap(in_page);
-			workspace->strm.avail_in = min(bytes_left,
-							   PAGE_SIZE);
-			workspace->strm.next_in = data_in;
-		}
+		if (workspace->strm.total_out > max_out)
+			break;
  	}
  	workspace->strm.avail_in = 0;
-	ret = zlib_deflate(&workspace->strm, Z_FINISH);
-	zlib_deflateEnd(&workspace->strm);
-
-	if (ret != Z_STREAM_END) {
-		ret = -EIO;
-		goto out;
+	/*
+	 * Call deflate with Z_FINISH flush parameter providing more output
+	 * space but no more input data, until it returns with Z_STREAM_END.
+	 */
+	while (ret != Z_STREAM_END) {
+		ret = zlib_deflate(&workspace->strm, Z_FINISH);
+		if (ret == Z_STREAM_END)
+			break;
+		if (ret != Z_OK && ret != Z_BUF_ERROR) {
+			zlib_deflateEnd(&workspace->strm);
+			ret = -EIO;
+			goto out;
+		} else if (workspace->strm.avail_out == 0) {
+			/* get another page for the stream end */
+			kunmap(out_page);
+			if (nr_pages == nr_dest_pages) {
+				out_page = NULL;
+				ret = -E2BIG;
+				goto out;
+			}
+			out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
+			if (out_page == NULL) {
+				ret = -ENOMEM;
+				goto out;
+			}

Do we need zlib_deflateEnd() for the above error cases?  Thanks,

Josef






