RFC Swap token re-tuned

Hi,
Here's a brief up on the next two mails.

PATCH 1:

In the current implementation of swap token tuning, grab swap token is made from :
1) after page_cache_read (filemap.c) and
2) after the readahead logic in do_swap_page (memory.c)

IMO, the contention for the swap token should happen _before_ the aforementioned calls, because in the event of low system memory, calls to freeup space will be made later from page_cache_read and read_swap_cache_async , so we want to avoid "false LRU" pages by grabbing the token before the VM starts searching for replacement candidates.

PATCH 2:

Instead of using TIMEOUT as a parameter to transfer the token, I think a better solution is to hand it over to a process that proves its eligibilty.

What my scheme does, is to find out how frequently a process is calling these functions. The processes that call these more frequently get a higher priority.
The idea is to guarantee that a high priority process gets the token. The priority of a process is determined by the number of consecutive calls to swap-in and no-page. I mean "consecutive" not from the scheduler point of view, but from the process point of view. In other words, if the task called these functions every time it was scheduled, it means it is not getting any further with its execution.

This way, its a matter of simple comparison of task priorities, to decide whether to transfer the token or not.

I did some testing with the two patches combined and the results are as follows:

Current Upstream implementation:
===============================

root@ashbert:~/crap# time ./qsbench -n 9000000 -p 3 -s 1420300
seed = 1420300
seed = 1420300
seed = 1420300

real    3m40.124s
user    0m12.060s
sys     0m0.940s

-------------reboot-----------------

With my implementation :
========================

root@ashbert:~/crap# time ./qsbench -n 9000000 -p 3 -s 1420300
seed = 1420300
seed = 1420300
seed = 1420300

real    2m58.708s
user    0m11.880s
sys     0m1.070s

My test machine:

1.69Ghz CPU
64M RAM
7200rpm hdd
2MB L2 cache
vanilla kernel 2.6.18
Ubuntu dapper with gnome.

Any comments, suggestions, ideas ?

Cheers,
Ashwin

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