zsmalloc: rework zspage chain size selection

zsmalloc: rework zspage chain size selection

Patch series "zsmalloc: make zspage chain size configurable".

Computers are bad at division.  We currently decide the best zspage chain
size (max number of physical pages per-zspage) by looking at a `used
percentage` value.  This is not enough as we lose precision during usage
percentage calculations For example, let's look at size class 208:

pages per zspage       wasted bytes         used%
       1                   144               96
       2                    80               99
       3                    16               99
       4                   160               99

Current algorithm will select 2 page per zspage configuration, as it's the
first one to reach 99%.  However, 3 pages per zspage waste less memory.

Change algorithm and select zspage configuration that has lowest wasted
value.

Link: https://lkml.kernel.org/r/20230118005210.2814763-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20230118005210.2814763-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>