Messages in this thread | | | Date | Fri, 29 Jul 2011 16:40:31 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH] kswapd: avoid unnecessary rebalance after an unsuccessful balancing |
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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 SUSE Labs
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