Re: [PATCH v3 01/23] multifd: Delete useless operation

[Juan Quintela]

"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> * Juan Quintela (quintela@redhat.com) wrote:
>> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
>> > * Juan Quintela (quintela@redhat.com) wrote:
>> >> We are divining by page_size to multiply again in the only use.
>> >              ^--- typo
>> >> Once there, impreve the comments.
>> >                   ^--- typo
>> >> 
>> >> Signed-off-by: Juan Quintela <quintela@redhat.com>
>> >
>> > OK, with the typo's fixed:
>> 
>> Thanks.
>> 
>> > Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>> >
>> > but, could you also explain the  x 2 (that's no worse than the current
>> > code); is this defined somewhere in zlib?  I thought there was a routine
>> > that told you the worst case?
>> 
>> Nowhere.
>> 
>> There are pathological cases where it can be worse.  Not clear at all
>> how much (ok, for zlib it appears that it is on the order of dozen of
>> bytes, because it marks it as uncompressed on the worst possible case),
>> For zstd, there is not a clear/fast answer when you google.
>
> For zlib:
>
> ZEXTERN uLong ZEXPORT compressBound OF((uLong sourceLen));
> /*
>      compressBound() returns an upper bound on the compressed size after
>    compress() or compress2() on sourceLen bytes.  It would be used before a
>    compress() or compress2() call to allocate the destination buffer.
> */

Aha, exaactly what I needed.

thanks.

zstd one is called:

ZSTD_compressBound()

Added to the series.

Thanks, Juan.