[lc-checkins] CVS: linux/include/linux comp_cache.h,1.37,1.38

[Rodrigo S. de C. <rc...@us...>]

Update of /cvsroot/linuxcompressed/linux/include/linux
In directory usw-pr-cvs1:/tmp/cvs-serv25332/include/linux

Modified Files:
	comp_cache.h 
Log Message:
Some changes regarding code optimization. These modifications have improved
a lot some tests (fillmem) we performed to test our current code.

- hash function changed to be arch-independent (by using SWP_OFFSET) and
also has been improved (shifting one position to the left).

- hash table size is in function of COMP_CACHE_CACHE_SIZE. It was set to a
static value and that hurts performance pretty badly for bigger sizes of
compressed cache. This change breaks the kernel parameter compsize=, but I
don't know if it's worth to add a variable to hold the hash table size since
the macro that uses this value (fragment_hashfn) is called many times.

- now the option in kernel config menu warns about the need of having a
maximum size of compressed cache as a power of two number for this hash
table size. If it's not a power of two, it breaks the hash function and the
performance drops heavily. To solve this problem, we could add a variable
that would be set to a reasonable value (a power of two) and in function of
the maximum size of the compressed cache, but there's the problem explained
above.

- swap_out_fragments() never sleeps to lock a page. If it couldn't be locked
at once, move it to the end of the LRU list and tries to lock the next.

- removed checksum from the comp_cache_fragment_t and checksum computation
from get_comp_cache_page() and decompress_page(). It added a huge overhead
in our tests.



Index: comp_cache.h
===================================================================
RCS file: /cvsroot/linuxcompressed/linux/include/linux/comp_cache.h,v
retrieving revision 1.37
retrieving revision 1.38
diff -C2 -r1.37 -r1.38
*** comp_cache.h	2002/01/02 16:59:05	1.37
--- comp_cache.h	2002/01/04 22:24:07	1.38
***************
*** 2,6 ****
   * linux/mm/comp_cache.h
   *
!  * Time-stamp: <2002-01-02 12:06:10 rcastro>
   *  
   * Linux Virtual Memory Compressed Cache
--- 2,6 ----
   * linux/mm/comp_cache.h
   *
!  * Time-stamp: <2002-01-04 19:31:48 rcastro>
   *  
   * Linux Virtual Memory Compressed Cache
***************
*** 29,32 ****
--- 29,33 ----
  #include <linux/WKcommon.h>
  
+ /* maximum compressed size of a page */
  #define MAX_COMPRESSED_SIZE 4500
  
***************
*** 58,62 ****
  	/* index == 0 && compressed_size != 0 => compressed_size = free_space */
  	unsigned short compressed_size;
- 	unsigned int checksum;
  	unsigned long flags;
  
--- 59,62 ----
***************
*** 489,494 ****
  inline void check_all_fragments(comp_cache_t *);
  
! #define HTABLE_SIZE 32
! #define hashfn(entry) ((entry >> 9) & (HTABLE_SIZE - 1))
  
  inline void add_fragment_to_hash_table(comp_cache_fragment_t *);
--- 489,494 ----
  inline void check_all_fragments(comp_cache_t *);
  
! #define FRAGMENT_HASH_SIZE (CONFIG_COMP_CACHE_SIZE/8)
! #define fragment_hashfn(entry) ((SWP_OFFSET(entry) >> 2) & (FRAGMENT_HASH_SIZE - 1))
  
  inline void add_fragment_to_hash_table(comp_cache_fragment_t *);