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

[Zaslonko Mikhail <zaslonko@linux.ibm.com>]

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)
>