Messages in this thread | | | Date | Sat, 17 Nov 2001 16:54:41 +0100 | From | Andrea Arcangeli <> | Subject | Re: 2.4.>=13 VM/kswapd/shmem/Oracle issue (was Re: Google's mm problems) |
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[ sorry for the delay ]
On Thu, Nov 15, 2001 at 05:48:36PM +0000, Arjan van de Ven wrote: > Andrea Arcangeli wrote: > > > loop that can trigger with the -ac VM when all the ZONE_DMA is > > unfreeable (now fixed in mainline with classzone) have nothing to do > > Ok I think I've misunderstood classzone then. > As I understand it, it prevents looping in ZONE_NORMAL when ZONE_DMA has > memory free, > and looping in ZONE_HIGHMEM if ZONE_NORMAL or ZONE_DMA have memory free.
correct.
> Can you please explain how it also solves the ZONE_DMA problem ?
It also solves the ZONE_DMA problem with the ->need_balance trigger in combination with the classzone logic.
With classzone in combination with the need_balance kswapd will never ever waste time trying to balance a never used classzone.
If all your hardware is PCI nobody will make an allocation from the ZONE_DMA classzone and so kswapd will never loop on the ZONE_DMA, as instead can happen with -ac as soon as the ZONE_DMA becomes unfreeable and under the low watermark (and "unfreeable" of course also means all anon not locked memory but no swap installed in the machine).
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