Messages in this thread |  | | Date | Tue, 25 Nov 2008 04:12:12 +0900 | From | "KOSAKI Motohiro" <> | Subject | Re: [PATCH -mm] vmscan: bail out of page reclaim after swap_cluster_max pages |
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>> Rik, sorry, I nak current your patch. because it don't fix old akpm issue. > > You are right. We do need to keep pressure between zones > equivalent to the size of the zones (or more precisely, to > the number of pages the zones have on their LRU lists).
Oh, sorry. you are right. but I talked about reverse thing.
1. shrink_zones() doesn't have any shortcut exiting way. it always call all zone's shrink_zone() 2. balance_pgdat also doesn't have shortcut.
simple shrink_zone() shortcut and lite memory pressure cause following bad scenario.
1. reclaim 32 page from ZONE_HIGHMEM 2. reclaim 32 page from ZONE_NORMAL 3. reclaim 32 page from ZONE_DMA 4. exit reclaim 5. another task call page alloc and it cause try_to_free_pages() 6. reclaim 32 page from ZONE_HIGHMEM 7. reclaim 32 page from ZONE_NORMAL 8. reclaim 32 page from ZONE_DMA
oops, all zone reclaimed the same pages although ZONE_HIGHMEM have much memory than ZONE_DMA. IOW, ZONE_DMA's reclaim scanning rate is much than ZONE_HIGHMEM largely.
it isn't intentionally.
Actually, try_to_free_pages don't need pressure fairness. it is the role of the balance_pgdat().
> However, having dozens of direct reclaim tasks all getting > to the lower priority levels can be disastrous, causing > extraordinarily large amounts of memory to be swapped out > and minutes-long stalls to applications.
agreed.
> > I think we can come up with a middle ground here: > - always let kswapd continue its rounds
agreed.
> - have direct reclaim tasks continue when priority == DEF_PRIORITY
disagreed. it cause above bad scenario, I think.
> - break out of the loop for direct reclaim tasks, when > priority < DEF_PRIORITY and enough pages have been freed > > Does that sound like it would mostly preserve memory pressure > between zones, while avoiding the worst of the worst when it > comes to excessive page eviction?
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