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Date: Sat, 9 May 2020 09:56:31 +0800 From: Chao Yu <yuchao0@...wei.com> To: Gao Xiang <hsiangkao@....com> CC: <jaegeuk@...nel.org>, <linux-kernel@...r.kernel.org>, <linux-f2fs-devel@...ts.sourceforge.net>, <chao@...nel.org> Subject: Re: [f2fs-dev] [PATCH] f2fs: compress: allow lz4 to compress data partially Hi Xiang, On 2020/5/8 18:23, Gao Xiang wrote: > Hi Chao, > > On Fri, May 08, 2020 at 05:47:09PM +0800, Chao Yu wrote: >> For lz4 worst compress case, caller should allocate buffer with size >> of LZ4_compressBound(inputsize) for target compressed data storing. >> >> However lz4 supports partial data compression, so we can get rid of >> output buffer size limitation now, then we can avoid 2 * 4KB size >> intermediate buffer allocation when log_cluster_size is 2, and avoid >> unnecessary compressing work of compressor if we can not save at >> least 4KB space. >> >> Suggested-by: Daeho Jeong <daehojeong@...gle.com> >> Signed-off-by: Chao Yu <yuchao0@...wei.com> >> --- >> fs/f2fs/compress.c | 15 +++++++++------ >> 1 file changed, 9 insertions(+), 6 deletions(-) >> >> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c >> index 5e4947250262..23825f559bcf 100644 >> --- a/fs/f2fs/compress.c >> +++ b/fs/f2fs/compress.c >> @@ -228,7 +228,12 @@ static int lz4_init_compress_ctx(struct compress_ctx *cc) >> if (!cc->private) >> return -ENOMEM; >> >> - cc->clen = LZ4_compressBound(PAGE_SIZE << cc->log_cluster_size); >> + /* >> + * we do not change cc->clen to LZ4_compressBound(inputsize) to >> + * adapt worst compress case, because lz4 algorithm supports partial >> + * compression. > > Actually, in this case the lz4 compressed block is not valid (at least not ended > in a valid lz4 EOF), and AFAIK the current public lz4 API cannot keep on > compressing this block. so IMO "partial compression" for an invalid lz4 > block may be confusing. Yes, comments could be improved to avoid confusing. > > I think some words like "because lz4 implementation can handle output buffer > budget properly" or similar stuff could be better. It's better, let me change to use this, thanks for the advice. Thanks, > > The same to the patch title and the commit message. > > Thanks, > Gao Xiang > > >> + */ >> + cc->clen = cc->rlen - PAGE_SIZE - COMPRESS_HEADER_SIZE; >> return 0; >> } >> >> @@ -244,11 +249,9 @@ static int lz4_compress_pages(struct compress_ctx *cc) >> >> len = LZ4_compress_default(cc->rbuf, cc->cbuf->cdata, cc->rlen, >> cc->clen, cc->private); >> - if (!len) { >> - printk_ratelimited("%sF2FS-fs (%s): lz4 compress failed\n", >> - KERN_ERR, F2FS_I_SB(cc->inode)->sb->s_id); >> - return -EIO; >> - } >> + if (!len) >> + return -EAGAIN; >> + >> cc->clen = len; >> return 0; >> } >> -- >> 2.18.0.rc1 > . >
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