[PATCH] btrfs: Convert zlib_compress_pages() to use kmap_local_page()

Fabio M. De Francesco
2022-06-27T16:33:16Z

The use of kmap() is being deprecated in favor of kmap_local_page(). With
kmap_local_page(), the mapping is per thread, CPU local and not globally
visible.

Therefore, use kmap_local_page() / kunmap_local() in zlib_compress_pages()
because in this function the mappings are per thread and are not visible
in other contexts. Furthermore, drop the mappings of "out_page" which is
allocated within zlib_compress_pages() with alloc_page(GFP_NOFS) and use
page_address() (thanks to David Sterba).

Tested with xfstests on a QEMU + KVM 32-bits VM with 4GB of RAM booting
a kernel with HIGHMEM64G enabled. This patch passes 26/26 tests of group
"compress".

Cc: Qu Wenruo <wqu@suse.com>
Suggested-by: David Sterba <dsterba@suse.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
fs/btrfs/zlib.c | 32 +++++++++++++-------------------
1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
index 770c4c6bbaef..b4f44662cda7 100644
--- a/fs/btrfs/zlib.c
+++ b/fs/btrfs/zlib.c
@@ -97,7 +97,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
{
struct workspace *workspace = list_entry(ws, struct workspace, list);
int ret;
- char *data_in;
+ char *data_in = NULL;
char *cpage_out;
int nr_pages = 0;
struct page *in_page = NULL;
@@ -126,7 +126,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
ret = -ENOMEM;
goto out;
}
- cpage_out = kmap(out_page);
+ cpage_out = page_address(out_page);
pages[0] = out_page;
nr_pages = 1;

@@ -148,26 +148,26 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
int i;

for (i = 0; i < in_buf_pages; i++) {
- if (in_page) {
- kunmap(in_page);
+ if (data_in) {
+ kunmap_local(data_in);
put_page(in_page);
}
in_page = find_get_page(mapping,
start >> PAGE_SHIFT);
- data_in = kmap(in_page);
+ data_in = kmap_local_page(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);
+ if (data_in) {
+ kunmap_local(data_in);
put_page(in_page);
}
in_page = find_get_page(mapping,
start >> PAGE_SHIFT);
- data_in = kmap(in_page);
+ data_in = kmap_local_page(in_page);
start += PAGE_SIZE;
workspace->strm.next_in = data_in;
}
@@ -196,9 +196,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
* the stream end if required
*/
if (workspace->strm.avail_out == 0) {
- kunmap(out_page);
if (nr_pages == nr_dest_pages) {
- out_page = NULL;
ret = -E2BIG;
goto out;
}
@@ -207,7 +205,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
ret = -ENOMEM;
goto out;
}
- cpage_out = kmap(out_page);
+ cpage_out = page_address(out_page);
pages[nr_pages] = out_page;
nr_pages++;
workspace->strm.avail_out = PAGE_SIZE;
@@ -234,9 +232,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
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;
}
@@ -245,7 +241,7 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
ret = -ENOMEM;
goto out;
}
- cpage_out = kmap(out_page);
+ cpage_out = page_address(out_page);
pages[nr_pages] = out_page;
nr_pages++;
workspace->strm.avail_out = PAGE_SIZE;
@@ -264,13 +260,11 @@ int zlib_compress_pages(struct list_head *ws, struct address_space *mapping,
*total_in = workspace->strm.total_in;
out:
*out_pages = nr_pages;
- if (out_page)
- kunmap(out_page);
-
- if (in_page) {
- kunmap(in_page);
+ if (data_in) {
+ kunmap_local(data_in);
put_page(in_page);
}
+
return ret;
}

--
2.36.1