compressed data will be usually loaded into last pages of
the extent (the last page for 4k) for in-place decompression
(more specifically, in-place IO), as ilustration below,
start of compressed logical extent
| end of this logical extent
| |
______v___________________________v________
... | page 6 | page 7 | page 8 | page 9 | ...
|__________|__________|__________|__________|
. ^ . ^
. |compressed|
. | data |
. . .
|< dstsize >|<margin>|
oend iend
op ip
Therefore, it's possible to do decompression inplace (thus no
memcpy at all) if the margin is sufficient and safe enough [1],
and it can be implemented only for fixed-size output compression
compared with fixed-size input compression.
No memcpy for most of in-place IO (about 99% of enwik9) after
decompression inplace is implemented and sequential read will
be improved of course (see the following patch for test results).
[1] https://github.com/lz4/lz4/commit/b17f578a919b7e6b078cede2d52be29dd48c8e8c
https://github.com/lz4/lz4/commit/5997e139f53169fa3a1c1b4418d2452a90b01602
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
drivers/staging/erofs/compress.h | 1 +
drivers/staging/erofs/decompressor.c | 21 ++++++++++++++++++---
drivers/staging/erofs/erofs_fs.h | 3 ++-
3 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/drivers/staging/erofs/compress.h b/drivers/staging/erofs/compress.h
index ebeccb1f4eae..c43aa3374d28 100644
--- a/drivers/staging/erofs/compress.h
+++ b/drivers/staging/erofs/compress.h
@@ -17,6 +17,7 @@ enum {
};
struct z_erofs_decompress_req {
+ struct super_block *sb;
struct page **in, **out;
unsigned short pageofs_out;
diff --git a/drivers/staging/erofs/decompressor.c b/drivers/staging/erofs/decompressor.c
index 4f644bdea0bc..727bae6a3cb0 100644
--- a/drivers/staging/erofs/decompressor.c
+++ b/drivers/staging/erofs/decompressor.c
@@ -14,6 +14,9 @@
#endif
#define LZ4_MAX_DISTANCE_PAGES DIV_ROUND_UP(LZ4_DISTANCE_MAX, PAGE_SIZE)
+#ifndef LZ4_DECOMPRESS_INPLACE_MARGIN
+#define LZ4_DECOMPRESS_INPLACE_MARGIN(srcsize) (((srcsize) >> 8) + 32)
+#endif
struct z_erofs_decompressor {
/*
@@ -131,9 +134,21 @@ static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
copied = false;
inlen = rq->inputsize - inputmargin;
if (rq->inplace_io) {
- src = generic_copy_inplace_data(rq, src, inputmargin);
- inputmargin = 0;
- copied = true;
+ const uint oend = (rq->pageofs_out +
+ rq->outputsize) & ~PAGE_MASK;
+ const uint nr = PAGE_ALIGN(rq->pageofs_out +
+ rq->outputsize) >> PAGE_SHIFT;
+
+ if (rq->partial_decoding ||
+ !(EROFS_SB(rq->sb)->requirements &
+ EROFS_REQUIREMENT_LZ4_0PADDING) ||
+ rq->out[nr - 1] != rq->in[0] ||
+ rq->inputsize - oend <
+ LZ4_DECOMPRESS_INPLACE_MARGIN(inlen)) {
+ src = generic_copy_inplace_data(rq, src, inputmargin);
+ inputmargin = 0;
+ copied = true;
+ }
}
ret = LZ4_decompress_safe_partial(src + inputmargin, out,
diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
index a05139f1df60..353322a3206c 100644
--- a/drivers/staging/erofs/erofs_fs.h
+++ b/drivers/staging/erofs/erofs_fs.h
@@ -21,7 +21,8 @@
* Any bits that aren't in EROFS_ALL_REQUIREMENTS should be
* incompatible with this kernel version.
*/
-#define EROFS_ALL_REQUIREMENTS 0
+#define EROFS_REQUIREMENT_LZ4_0PADDING 0x00000001
+#define EROFS_ALL_REQUIREMENTS EROFS_REQUIREMENT_LZ4_0PADDING
struct erofs_super_block {
/* 0 */__le32 magic; /* in the little endian */
--
2.17.1
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