Re: [PATCHv7 10/24] zram: add zlib compression backend support

Sergey Senozhatsky
2025-05-09T01:38:19Z

Hello,

On (25/05/08 16:19), Zaslonko Mikhail wrote:
[..]
> > +#include "backend_deflate.h"
> > +
> > +/* Use the same value as crypto API */
> > +#define DEFLATE_DEF_WINBITS 11
> > +#define DEFLATE_DEF_MEMLEVEL MAX_MEM_LEVEL
> > +
[..]
> The comment line says 'Use the same value as crypto API'...
> could you please clarify here? Are there some memory constraints?

When zram transitioned from Crypto API (scomp) to custom compression
API I picked the CryptoAPI deflate DEFLATE_DEF_WINBITS value:

crypto/deflate.c: DEFLATE_DEF_WINBITS 11

which is then passed to zlib_deflateInit2() and zlib_inflateInit2().

> I tried to build the kernel with DEFLATE_DEF_WINBITS set to 15 and
> verified that s390 hardware deflate acceleration works for zram devices
> with a deflate compression.

If we define it as 15 on non-s390 machines, will there be any
consequences? Increased memory usage? By how much?