JFFS2 memLevel and windowBits

[Karl(Kai) Ji]

Hi all,

I am working on a VZ-board with 8MB DRAM and using uClinux-2.4.17 as kernel.
It is using JFFS2 to operate its FLASH(2MB) As a no-mmu system, memory
fragmation becomes a headache for a stable performace. So I am trying to
tune down memory usage by lower variable `memLevel' and `windowBits'.  the
default value for memLevel is 8 and windowBits=15. 
memLevel=7 and windowBits=15 seems to be ok but memLevel=8 and windowBits=14
unfortunately do not work. Why is that? From reading the comments in
zlib.h/zconf.h seems such modification is allowed.  

/* The memory requirements for deflate are (in bytes):
            (1 << (windowBits+2)) +  (1 << (memLevel+9))
 that is: 128K for windowBits=15  +  128K for memLevel = 8  (default values)
 plus a few kilobytes for small objects. For example, if you want to reduce
 the default memory requirements from 256K to 128K, compile with
     make CFLAGS="-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7"
 Of course this will generally degrade compression (there's no free lunch).

   The memory requirements for inflate are (in bytes) 1 << windowBits
 that is, 32K for windowBits=15 (default value) plus a few kilobytes
 for small objects.
*/

Any hints is appreciated.

Karl