On 2020/5/8 11:30, Daeho Jeong wrote:
> I am a little bit confused.
>
> In compress_log=2 (4 pages),
>
> Every compression algorithm will set the cc->nr_cpages to 5 pages like below.
>
> max_len = COMPRESS_HEADER_SIZE + cc->clen;
> cc->nr_cpages = DIV_ROUND_UP(max_len, PAGE_SIZE);
>
> cc->cpages = f2fs_kzalloc(sbi, sizeof(struct page *) *
> cc->nr_cpages, GFP_NOFS);
>
> And call cops->compress_pages(cc) and the returned length of the compressed
> data will be set to cc->clen for every case.
> And if the cc->clen is larger than max_len, we will give up compression.
>
> ret = cops->compress_pages(cc);
> if (ret)
> goto out_vunmap_cbuf;
>
> max_len = PAGE_SIZE * (cc->cluster_size - 1) - COMPRESS_HEADER_SIZE;
>
> if (cc->clen > max_len) {
> ret = -EAGAIN;
> goto out_vunmap_cbuf;
> }
>
> So, with your patch, we will just use 3 pages for ZSTD and 5 pages for LZO
> and LZ4 now.
> My question was whether it is also possible to decrease the compression
> buffer size for LZO and LZ4 to 3 pages like ZSTD case.
> I was just curious about that. :)
I guess we can change LZ4 as we did for ZSTD case, since it supports partially
compression:
- lz4_compress_pages
- LZ4_compress_default
- LZ4_compress_fast
- LZ4_compress_fast_extState
if (maxOutputSize < LZ4_COMPRESSBOUND(inputSize))
- LZ4_compress_generic(..., limitedOutput, ...)
- if (outputLimited && boundary_check_condition) return 0;
And for LZO case, it looks we have to keep to allocate 5 pages for worst
compression case as it doesn't support partially compression as I checked.
Thanks,
>
>
> 2020년 5월 8일 (금) 오전 11:48, Chao Yu <yuch...@huawei.com
> <mailto:yuch...@huawei.com>>님이 작성:
>
> Hi Daeho,
>
> On 2020/5/8 9:28, Daeho Jeong wrote:
> > Hi Chao,
> >
> > IIUC, you are trying not to use ZSTD_compressBound() to save the memory
> > space. Am I right?
> >
> > Then, how about LZ4_compressBound() for LZ4 and lzo1x_worst_compress()
> for
> > LZO?
>
> Oops, it looks those limits were wrongly used...
>
> #define LZ4_COMPRESSBOUND(isize) (\
> (unsigned int)(isize) > (unsigned int)LZ4_MAX_INPUT_SIZE \
> ? 0 \
> : (isize) + ((isize)/255) + 16)
>
> #define lzo1x_worst_compress(x) ((x) + ((x) / 16) + 64 + 3 + 2)
>
> Newly calculated boundary size is larger than target buffer size.
>
> However comments on LZ4_compress_default() said:
>
> ...
> * @maxOutputSize: full or partial size of buffer 'dest'
> * which must be already allocated
> ...
> int LZ4_compress_default(const char *source, char *dest, int inputSize,
> int maxOutputSize, void *wrkmem);
>
> And @out_len in lzo1x_1_compress() was passed as an output parameter to
> pass length of data that compressor compressed into @out buffer.
>
> Let me know if I missed sth.
>
> Thannks,
>
> > Could we save more memory space for these two cases like ZSTD?
> > As you know, we are using 5 pages compression buffer for LZ4 and LZO in
> > compress_log_size=2,
> > and if the compressed data doesn't fit in 3 pages, it returns -EAGAIN to
> > give up compressing that one.
> >
> > Thanks,
> >
> > 2020년 5월 8일 (금) 오전 10:17, Chao Yu <yuch...@huawei.com
> <mailto:yuch...@huawei.com>>님이 작성:
> >
> >> During zstd compression, ZSTD_endStream() may return non-zero value
> >> because distination buffer is full, but there is still compressed data
> >> remained in intermediate buffer, it means that zstd algorithm can not
> >> save at last one block space, let's just writeback raw data instead of
> >> compressed one, this can fix data corruption when decompressing
> >> incomplete stored compression data.
> >>
> >> Signed-off-by: Daeho Jeong <daehoje...@google.com
> <mailto:daehoje...@google.com>>
> >> Signed-off-by: Chao Yu <yuch...@huawei.com <mailto:yuch...@huawei.com>>
> >> ---
> >> fs/f2fs/compress.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >>
> >> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
> >> index c22cc0d37369..5e4947250262 100644
> >> --- a/fs/f2fs/compress.c
> >> +++ b/fs/f2fs/compress.c
> >> @@ -358,6 +358,13 @@ static int zstd_compress_pages(struct compress_ctx
> >> *cc)
> >> return -EIO;
> >> }
> >>
> >> + /*
> >> + * there is compressed data remained in intermediate buffer
> due to
> >> + * no more space in cbuf.cdata
> >> + */
> >> + if (ret)
> >> + return -EAGAIN;
> >> +
> >> cc->clen = outbuf.pos;
> >> return 0;
> >> }
> >> --
> >> 2.18.0.rc1
> >>
> >>
> >>
> >> _______________________________________________
> >> Linux-f2fs-devel mailing list
> >> linux-f2fs-de...@lists.sourceforge.net
> <mailto:linux-f2fs-de...@lists.sourceforge.net>
> >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >>
> >
>
