On 2019/6/21 0:07, Gao Xiang wrote: > 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 > > Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
