[lkml]   [2011]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] kswapd: avoid unnecessary rebalance after an unsuccessful balancing
On Fri, Jul 29, 2011 at 11:23:10PM +0800, Alex Shi wrote:
> In commit 215ddd66, Mel Gorman said kswapd is better to sleep after a
> unsuccessful balancing if there is tighter reclaim request pending in
> the balancing. In this scenario, the 'order' and 'classzone_idx'
> that are checked for tighter request judgment is incorrect, since they
> aren't the one kswapd should read from new pgdat, but the last time pgdat
> value for just now balancing. Then kswapd will skip try_to_sleep func
> and rebalance the last pgdat request. It's not our expected behavior.
> So, I added new variables to distinguish the returned order/classzone_idx
> from last balancing, that can resolved above issue in that scenario.

I'm afraid this changelog is very difficult to read and I do not see
what problem you are trying to solve and I do not see what this patch
might solve.

When balance_pgdat() returns with a lower classzone or order, the values
stored in pgdat are not re-read and instead it tries to go to sleep
based on the starting request. Something like;

1. Read pgdat request A (classzone_idx, order)
2. balance_pgdat()
3. During pgdat, a new pgdat request B (classzone_idx, order) is placed
4. balance_pgdat() returns but failed so classzone_idx is lower
5. Try to sleep based on pgdat request A

i.e. pgdat request B is not read and there is a comment explaining
why pgdat request B is not read after balance_pgdat() fails.

This patch adds some variables that might improve the readability
for some people but otherwise I can't see what problem is being
fixed. What did I miss?

Mel Gorman

 \ /
  Last update: 2011-07-29 17:43    [W:0.060 / U:2.732 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site