Re: [PATCH v9 14/19] zsmalloc: introduce new object mapping API

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (25/03/01 15:22), Herbert Xu wrote:
> Sergey Senozhatsky <senozhatsky@chromium.org> wrote:
> >
> > New API splits functions by access mode:
> > - zs_obj_read_begin(handle, local_copy)
> >  Returns a pointer to handle memory.  For objects that span two
> >  physical pages a local_copy buffer is used to store object's
> >  data before the address is returned to the caller.  Otherwise
> >  the object's page is kmap_local mapped directly.
> 
> I presume this buffer is always given to the compression algorithm
> to decompress? In that case there should be no need to linearise
> them at all.
> 
> Just return a two-entry SG list, and give it to the Crypto API
> to deal with.  Both software and hardware algorithms can handle
> non-linear input.  Yes software decompression is currently
> linearising all input with a copy, but that is no different
> to the copy that you're making in zsmalloc.
> 
> So please change this API to create an SG list instead of copying.
> That way we can then optimise the software decompression to read
> non-linear input directly and skip the copying altogether.

A heads up:

Discussed with Herbert privately, we will look into SG-list API
later (future dev cycles).