[PATCH 5/5] btrfs: Increase buffer size for zlib functions

Mikhail Zaslonko
2019-11-26T14:41:46Z

Due to the small size of zlib buffer (1 page) set in btrfs code, s390
hardware compression is rather limited in terms of performance. Increasing
the buffer size to 4 pages would bring significant benefit for s390
hardware compression (up to 60% better performance compared to the
PAGE_SIZE buffer) and should not bring much overhead in terms of memory
consumption due to order 2 allocations.

Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
---
fs/btrfs/compression.c | 2 +-
fs/btrfs/zlib.c | 109 ++++++++++++++++++++++++++---------------
2 files changed, 70 insertions(+), 41 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index b05b361e2062..f789b356fd8b 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1158,7 +1158,7 @@ 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 df1aace5df50..c5b4654e1242 100644
--- a/fs/btrfs/zlib.c
+++ b/fs/btrfs/zlib.c
@@ -20,6 +20,8 @@
#include <linux/refcount.h>
#include "compression.h"

+#define ZLIB_BUF_SIZE (4 * PAGE_SIZE)
+
struct workspace {
z_stream strm;
char *buf;
@@ -76,7 +78,7 @@ static 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 = kmalloc(ZLIB_BUF_SIZE, GFP_KERNEL);
if (!workspace->strm.workspace || !workspace->buf)
goto fail;

@@ -97,6 +99,7 @@ static int zlib_compress_pages(struct list_head *ws,
unsigned long *total_out)
{
struct workspace *workspace = list_entry(ws, struct workspace, list);
+ int i;
int ret;
char *data_in;
char *cpage_out;
@@ -104,6 +107,7 @@ static int zlib_compress_pages(struct list_head *ws,
struct page *in_page = NULL;
struct page *out_page = NULL;
unsigned long bytes_left;
+ unsigned long 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;
@@ -121,9 +125,6 @@ static int zlib_compress_pages(struct list_head *ws,
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;
@@ -133,12 +134,34 @@ static int zlib_compress_pages(struct list_head *ws,
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 set of pages and copy their contents to
+ * the input buffer for the following deflate call
+ */
+ if (workspace->strm.avail_in == 0) {
+ bytes_left = len - workspace->strm.total_in;
+ in_buf_pages = min(DIV_ROUND_UP(bytes_left, PAGE_SIZE),
+ ZLIB_BUF_SIZE / PAGE_SIZE);
+ for (i = 0; i < in_buf_pages; i++) {
+ in_page = find_get_page(mapping,
+ start >> PAGE_SHIFT);
+ data_in = kmap(in_page);
+ memcpy(workspace->buf + i*PAGE_SIZE, data_in,
+ PAGE_SIZE);
+ kunmap(in_page);
+ put_page(in_page);
+ start += PAGE_SIZE;
+ }
+ workspace->strm.avail_in = min(bytes_left,
+ ZLIB_BUF_SIZE);
+ workspace->strm.next_in = workspace->buf;
+ }
+
ret = zlib_deflate(&workspace->strm, Z_SYNC_FLUSH);
if (ret != Z_OK) {
pr_debug("BTRFS: deflate in loop returned %d\n",
@@ -149,12 +172,13 @@ static int zlib_compress_pages(struct list_head *ws,
}

/* we're making it bigger, give up */
- if (workspace->strm.total_in > 8192 &&
+ if (workspace->strm.total_in > ZLIB_BUF_SIZE &&
workspace->strm.total_in <
workspace->strm.total_out) {
ret = -E2BIG;
goto out;
}
+
/* we need another page for writing out. Test this
* before the total_in so we will pull in a new page for
* the stream end if required
@@ -180,33 +204,42 @@ static int zlib_compress_pages(struct list_head *ws,
/* 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;
+ }
+ cpage_out = kmap(out_page);
+ pages[nr_pages] = out_page;
+ nr_pages++;
+ workspace->strm.avail_out = PAGE_SIZE;
+ workspace->strm.next_out = cpage_out;
+ }
}
+ zlib_deflateEnd(&workspace->strm);

if (workspace->strm.total_out >= workspace->strm.total_in) {
ret = -E2BIG;
@@ -221,10 +254,6 @@ static int zlib_compress_pages(struct list_head *ws,
if (out_page)
kunmap(out_page);

- if (in_page) {
- kunmap(in_page);
- put_page(in_page);
- }
return ret;
}

@@ -250,7 +279,7 @@ static int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)

workspace->strm.total_out = 0;
workspace->strm.next_out = workspace->buf;
- workspace->strm.avail_out = PAGE_SIZE;
+ workspace->strm.avail_out = ZLIB_BUF_SIZE;

/* If it's deflate, and it's got no preset dictionary, then
we can tell zlib to skip the adler32 check. */
@@ -289,7 +318,7 @@ static int zlib_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
}

workspace->strm.next_out = workspace->buf;
- workspace->strm.avail_out = PAGE_SIZE;
+ workspace->strm.avail_out = ZLIB_BUF_SIZE;

if (workspace->strm.avail_in == 0) {
unsigned long tmp;
@@ -340,7 +369,7 @@ static int zlib_decompress(struct list_head *ws, unsigned char *data_in,
workspace->strm.total_in = 0;

workspace->strm.next_out = workspace->buf;
- workspace->strm.avail_out = PAGE_SIZE;
+ workspace->strm.avail_out = ZLIB_BUF_SIZE;
workspace->strm.total_out = 0;
/* If it's deflate, and it's got no preset dictionary, then
we can tell zlib to skip the adler32 check. */
@@ -384,7 +413,7 @@ static int zlib_decompress(struct list_head *ws, unsigned char *data_in,
buf_offset = 0;

bytes = min(PAGE_SIZE - pg_offset,
- PAGE_SIZE - buf_offset);
+ PAGE_SIZE - (buf_offset % PAGE_SIZE));
bytes = min(bytes, bytes_left);

kaddr = kmap_atomic(dest_page);
@@ -395,7 +424,7 @@ static int zlib_decompress(struct list_head *ws, unsigned char *data_in,
bytes_left -= bytes;
next:
workspace->strm.next_out = workspace->buf;
- workspace->strm.avail_out = PAGE_SIZE;
+ workspace->strm.avail_out = ZLIB_BUF_SIZE;
}

if (ret != Z_STREAM_END && bytes_left != 0)
--
2.17.1