Re: [PATCH 1/1] lz4: Implement lz4 with dynamic offset length.

Sergey Senozhatsky
2018-04-04T01:40:32Z

On (04/03/18 19:13), Vaneet Narang wrote:
> Hi Sergey,
>
> >You shrink a 2 bytes offset down to a 1 byte offset, thus you enforce that
> 2 Byte offset is not shrinked to 1 byte, Its only 1 bit is reserved out of
> 16 bits of offset. So only 15 Bits can be used to store offset value.

Yes, you are right. My bad, was thinking about something else.

> >'page should be less than 32KB', which I'm sure will be confusing.
> lz4_dyn will work on bigger data length(> 32k) but in that case compression
> ratio may not be better than LZ4. This is same as LZ4 compressing data more
> than 64K (16Bits). LZ4 can't store offset more than 64K similarly
> LZ4 dyn can't store offset more than 32K.

Then drop that `if PAGE_SIZE' thing. I'd rather do that stuff internally
in lz4... if it needed at all.

> >And you
> >rely on lz4_dyn users to do the right thing - namely, to use that 'nice'
> >`#if (PAGE_SIZE < (32 * KB))'.
> They don't need to add this code

Then drop it.

> >Apart from that, lz4_dyn supports only data
> >in up to page_size chunks. Suppose my system has page_size of less than 32K,
> >so I legitimately can enable lz4_dyn, but suppose that I will use it
> >somewhere where I don't work with page_size-d chunks. Will I able to just
> >do tfm->compress(src, sz) on random buffers? The whole thing looks to be
> >quite fragile.
> No thats not true, lz4_dyn can work for random buffers and it need not be
> of page size chunks. There is no difference in Lz4 and Lz4 dyn working.

You are right.

-ss