Re: [PATCH v2 6/6] btrfs: Use larger zlib buffer for s390 hardware compression

Zaslonko Mikhail
2019-12-13T16:10:26Z

Hello,

Could you please review the patch for btrfs below.

Apart from falling back to 1 page, I have set the condition to allocate
4-pages zlib workspace buffer only if s390 Deflate-Conversion facility
is installed and enabled. Thus, it will take effect on s390 architecture
only.

Currently in zlib_compress_pages() I always copy input pages to the workspace
buffer prior to zlib_deflate call. Would that make sense, to pass the page
itself, as before, based on the workspace buf_size (for 1-page buffer)?

As for calling zlib_deflate with Z_FINISH flush parameter in a loop until
Z_STREAM_END is returned, that comes in agreement with the zlib manual.

Please see for more details:
https://lkml.org/lkml/2019/12/9/537

Thanks,
Mikhail

On 09.12.2019 16:29, Mikhail Zaslonko wrote:
> 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 when s390 zlib hardware support is enabled
> would bring significant benefit to btrfs zlib (up to 60% better performance
> compared to the PAGE_SIZE buffer). In case of memory pressure we fall back
> to a single page buffer during workspace allocation.
>
> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
> ---
> fs/btrfs/compression.c | 2 +-
> fs/btrfs/zlib.c | 118 +++++++++++++++++++++++++++--------------
> 2 files changed, 80 insertions(+), 40 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..0bc0d57ba233 100644
> --- a/fs/btrfs/zlib.c
> +++ b/fs/btrfs/zlib.c
> @@ -20,9 +20,12 @@
> #include <linux/refcount.h>
> #include "compression.h"
>
> +#define ZLIB_DFLTCC_BUF_SIZE (4 * PAGE_SIZE)
> +
> struct workspace {
> z_stream strm;
> char *buf;
> + unsigned long buf_size;
> struct list_head list;
> int level;
> };
> @@ -76,7 +79,17 @@ 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 = NULL;
> + 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;
>
> @@ -97,6 +110,7 @@ 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 +118,7 @@ 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 +136,6 @@ 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 +145,34 @@ 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),
> + workspace->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,
> + workspace->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",
> @@ -155,6 +189,7 @@ static int zlib_compress_pages(struct list_head *ws,
> 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 +215,42 @@ 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 +265,6 @@ 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 +290,7 @@ 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 = workspace->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 +329,7 @@ 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 = workspace->buf_size;
>
> if (workspace->strm.avail_in == 0) {
> unsigned long tmp;
> @@ -340,7 +380,7 @@ 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 = workspace->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 +424,7 @@ 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 +435,7 @@ 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 = workspace->buf_size;
> }
>
> if (ret != Z_STREAM_END && bytes_left != 0)
>