Re: [PATCH v3 6/6] btrfs: Use larger zlib buffer for s390 hardware compression

Josef Bacik
2020-01-06T16:41:03Z

On 1/3/20 5:33 PM, 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.
>
> Signed-off-by: Mikhail Zaslonko <zaslonko@linux.ibm.com>
> ---
> fs/btrfs/compression.c | 2 +-
> fs/btrfs/zlib.c | 128 ++++++++++++++++++++++++++++++-----------
> 2 files changed, 94 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..159486801631 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;
> };
> @@ -61,7 +64,17 @@ 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;
>
> @@ -78,6 +91,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
> unsigned long *total_in, unsigned long *total_out)
> {
> struct workspace *workspace = list_entry(ws, struct workspace, list);
> + int i;
> int ret;
> char *data_in;
> char *cpage_out;
> @@ -85,6 +99,7 @@ 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 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;
> @@ -102,9 +117,6 @@ 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 +126,48 @@ 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) {
> + 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;
> + }

Is there a reason to leave the last in_page mapped here? I realize we'll clean
it up further down, but since we're copying everything into the buf anyway why
not just map->copy->unmap for everything?

> + 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,
> + workspace->buf_size);
> + }
> +
> ret = zlib_deflate(&workspace->strm, Z_SYNC_FLUSH);
> if (ret != Z_OK) {
> pr_debug("BTRFS: deflate in loop returned %d\n",
> @@ -136,6 +184,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
> ret = -E2BIG;
> goto out;
> }
> +

Extra newline. Thanks,

Josef