2022-06-01 19:18:22

by Fabio M. De Francesco

Subject: [PATCH 2/3] btrfs: Replace kmap() with kmap_local_page() in lzo.c

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

Therefore, use kmap_local_page() / kunmap_local() in lzo.c wherever the
mappings are per thread and not globally visible.

Tested on QEMU + KVM 32 bits VM with 4GB of RAM and HIGHMEM64G enabled.

Suggested-by: Ira Weiny <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
fs/btrfs/lzo.c | 28 ++++++++++++----------------
1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
index 430ad36b8b08..89bc5f825e0a 100644
--- a/fs/btrfs/lzo.c
+++ b/fs/btrfs/lzo.c
@@ -155,7 +155,7 @@ static int copy_compressed_data_to_page(char *compressed_data,
out_pages[*cur_out / PAGE_SIZE] = cur_page;
}

- kaddr = kmap(cur_page);
+ kaddr = kmap_local_page(cur_page);
write_compress_length(kaddr + offset_in_page(*cur_out),
compressed_size);
*cur_out += LZO_LEN;
@@ -167,7 +167,7 @@ static int copy_compressed_data_to_page(char *compressed_data,
u32 copy_len = min_t(u32, sectorsize - *cur_out % sectorsize,
orig_out + compressed_size - *cur_out);

- kunmap(cur_page);
+ kunmap_local(kaddr);

if ((*cur_out / PAGE_SIZE) >= max_nr_page)
return -E2BIG;
@@ -180,7 +180,7 @@ static int copy_compressed_data_to_page(char *compressed_data,
return -ENOMEM;
out_pages[*cur_out / PAGE_SIZE] = cur_page;
}
- kaddr = kmap(cur_page);
+ kaddr = kmap_local_page(cur_page);

memcpy(kaddr + offset_in_page(*cur_out),
compressed_data + *cur_out - orig_out, copy_len);
@@ -202,7 +202,7 @@ static int copy_compressed_data_to_page(char *compressed_data,
*cur_out += sector_bytes_left;

out:
- kunmap(cur_page);
+ kunmap_local(kaddr);
return 0;
}

@@ -248,12 +248,12 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping,
/* Compress at most one sector of data each time */
in_len = min_t(u32, start + len - cur_in, sectorsize - sector_off);
ASSERT(in_len);
- data_in = kmap(page_in);
+ data_in = kmap_local_page(page_in);
ret = lzo1x_1_compress(data_in +
offset_in_page(cur_in), in_len,
workspace->cbuf, &out_len,
workspace->mem);
- kunmap(page_in);
+ kunmap_local(data_in);
if (ret < 0) {
pr_debug("BTRFS: lzo in loop returned %d\n", ret);
ret = -EIO;
@@ -310,7 +310,6 @@ static void copy_compressed_segment(struct compressed_bio *cb,
u32 orig_in = *cur_in;

while (*cur_in < orig_in + len) {
- char *kaddr;
struct page *cur_page;
u32 copy_len = min_t(u32, PAGE_SIZE - offset_in_page(*cur_in),
orig_in + len - *cur_in);
@@ -318,11 +317,8 @@ static void copy_compressed_segment(struct compressed_bio *cb,
ASSERT(copy_len);
cur_page = cb->compressed_pages[*cur_in / PAGE_SIZE];

- kaddr = kmap(cur_page);
- memcpy(dest + *cur_in - orig_in,
- kaddr + offset_in_page(*cur_in),
- copy_len);
- kunmap(cur_page);
+ memcpy_from_page(dest + *cur_in - orig_in, cur_page,
+ offset_in_page(*cur_in), copy_len);

*cur_in += copy_len;
}
@@ -342,9 +338,9 @@ int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
/* Bytes decompressed so far */
u32 cur_out = 0;

- kaddr = kmap(cb->compressed_pages[0]);
+ kaddr = kmap_local_page(cb->compressed_pages[0]);
len_in = read_compress_length(kaddr);
- kunmap(cb->compressed_pages[0]);
+ kunmap_local(kaddr);
cur_in += LZO_LEN;

/*
@@ -378,9 +374,9 @@ int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
(cur_in + LZO_LEN - 1) / sectorsize);
cur_page = cb->compressed_pages[cur_in / PAGE_SIZE];
ASSERT(cur_page);
- kaddr = kmap(cur_page);
+ kaddr = kmap_local_page(cur_page);
seg_len = read_compress_length(kaddr + offset_in_page(cur_in));
- kunmap(cur_page);
+ kunmap_local(kaddr);
cur_in += LZO_LEN;

if (seg_len > WORKSPACE_CBUF_LENGTH) {
--
2.36.1

2022-06-01 20:02:24

by Christoph Hellwig

Subject: Re: [PATCH 2/3] btrfs: Replace kmap() with kmap_local_page() in lzo.c

On Tue, May 31, 2022 at 04:53:34PM +0200, Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page() where
> it is feasible. With kmap_local_page(), the mapping is per thread, CPU
> local and not globally visible.
>
> Therefore, use kmap_local_page() / kunmap_local() in lzo.c wherever the
> mappings are per thread and not globally visible.

This looks fine:

Reviewed-by: Christoph Hellwig <[email protected]>