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Commit 0ffd71bc authored by Gao Xiang's avatar Gao Xiang Committed by Greg Kroah-Hartman
Browse files

staging: erofs: introduce LZ4 decompression inplace 

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] https://github.com/lz4/lz4/commit/b17f578a919b7e6b078cede2d52be29dd48c8e8c
    https://github.com/lz4/lz4/commit/5997e139f53169fa3a1c1b4418d2452a90b01602



Reviewed-by: default avatarChao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarGao Xiang <gaoxiang25@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 7fc45dbc

drivers/staging/erofs/compress.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -17,6 +17,7 @@ enum { 
};

};





struct z_erofs_decompress_req {

struct z_erofs_decompress_req {

	struct super_block *sb;

	struct page **in, **out;

	struct page **in, **out;





	unsigned short pageofs_out;

	unsigned short pageofs_out;

drivers/staging/erofs/decompressor.c

+32 −4
Original line number Original line Diff line number Diff line
@@ -14,6 +14,9 @@ 
#endif

#endif





#define LZ4_MAX_DISTANCE_PAGES	DIV_ROUND_UP(LZ4_DISTANCE_MAX, PAGE_SIZE)

#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 {

struct z_erofs_decompressor {

	/*

	/*
@@ -112,7 +115,7 @@ static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out) 
{

{

	unsigned int inputmargin, inlen;

	unsigned int inputmargin, inlen;

	u8 *src;

	u8 *src;

	bool copied;

	bool copied, support_0padding;

	int ret;

	int ret;





	if (rq->inputsize > PAGE_SIZE)

	if (rq->inputsize > PAGE_SIZE)
@@ -120,14 +123,39 @@ static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out) 




	src = kmap_atomic(*rq->in);

	src = kmap_atomic(*rq->in);

	inputmargin = 0;

	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;

	copied = false;

	inlen = rq->inputsize - inputmargin;

	inlen = rq->inputsize - inputmargin;

	if (rq->inplace_io) {

	if (rq->inplace_io) {

		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);

			src = generic_copy_inplace_data(rq, src, inputmargin);

			inputmargin = 0;

			inputmargin = 0;

			copied = true;

			copied = true;

		}

		}

	}





	ret = LZ4_decompress_safe_partial(src + inputmargin, out,

	ret = LZ4_decompress_safe_partial(src + inputmargin, out,

					  inlen, rq->outputsize,

					  inlen, rq->outputsize,

drivers/staging/erofs/erofs_fs.h

+2 −1
Original line number Original line Diff line number Diff line
@@ -21,7 +21,8 @@ 
 * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be

 * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be

 * incompatible with this kernel version.

 * 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 {

struct erofs_super_block {

/*  0 */__le32 magic;           /* in the little endian */

/*  0 */__le32 magic;           /* in the little endian */