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

Josef Bacik
2020-01-08T15:08:33Z

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@linux.ibm.com>

> ---
> 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