Re: [PATCH] zram: add zstd to the supported algorithms list

[Sergey Senozhatsky]

On (08/25/17 02:09), Nick Terrell wrote:
[..]
> > > I think using dictionaries in zram could be very interesting. We could for
> > > example, take a random sample of the RAM and use that as the dictionary
> > > for compression. E.g. take 32 512B samples from RAM and build a 16 KB
> > > dictionary (sizes may vary).
> > > 
> > > I'm not sure how you would pass a dictionary into the crypto compression
> > > API, but I'm sure we can make something work if dictionary compression
> > > proves to be beneficial enough.
> > 
> > a dictionaty pointer can be in `struct zstd_ctx'.
> 
> Sorry I'm not super familiar with the crypto API. How would the user
> initialize the dictionary in the `struct zstd_ctx'? I guess you could
> either expose the struct in some header, or provide a function that
> initializes it, but that isn't generic. Does the crypto library already
> have a standard way to provide extra information?

not really familiar either... I was thinking about having "zstd" and
"zstd_dict" crypto_alg structs - one would be !dict, the other one would
allocate dict and pass it to compress/decompress zstd callbacks. "zstd"
vecrsion would invoke zstd_params() passing zeros as compress and dict
sizes to ZSTD_getParams(), while "zstd_dict" would invoke, lets say,
zstd_params_dict() passing PAGE_SIZE-s. hm... (0, PAGE_SIZE)?  to
ZSTD_getParams(). just a rough idea...

	-ss