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 <daehoje...@google.com>
>> Signed-off-by: Chao Yu <yuch...@huawei.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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