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Subject[RFC][PATCH 0/2] Swap token re-tuned
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Date

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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