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staging: erofs: introduce LZ4 decompression inplace

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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 patches for test results).

[1] b17f578a91
    5997e139f5

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Gao Xiang 2019-06-24 15:22:56 +08:00 committed by Greg Kroah-Hartman
parent 7fc45dbc93
commit 0ffd71bcc3
3 changed files with 35 additions and 5 deletions
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1
drivers/staging/erofs/compress.h
View File

@ -17,6 +17,7 @@ enum {
};
struct z_erofs_decompress_req {
struct super_block *sb;
struct page **in, **out;
unsigned short pageofs_out;

36
drivers/staging/erofs/decompressor.c
View File

@ -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 {
/*
@ -112,7 +115,7 @@ static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
{
unsigned int inputmargin, inlen;
u8 *src;
bool copied;
bool copied, support_0padding;
int ret;
if (rq->inputsize > PAGE_SIZE)
@ -120,13 +123,38 @@ static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
src = kmap_atomic(*rq->in);
inputmargin = 0;
support_0padding = false;
/* decompression inplace is only safe when 0padding is enabled */
if (EROFS_SB(rq->sb)->requirements & EROFS_REQUIREMENT_LZ4_0PADDING) {
support_0padding = true;
while (!src[inputmargin & ~PAGE_MASK])
if (!(++inputmargin & ~PAGE_MASK))
break;
if (inputmargin >= rq->inputsize) {
kunmap_atomic(src);
return -EIO;
}
}
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 || !support_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,

3
drivers/staging/erofs/erofs_fs.h
View File

@ -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 */