Messages in this thread | | | Date | Tue, 17 Nov 2009 00:07:44 -0800 (PST) | From | David Rientjes <> | Subject | Re: [PATCH 0/7] Kill PF_MEMALLOC abuse |
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On Tue, 17 Nov 2009, KOSAKI Motohiro wrote:
> > PF_MEMALLOC have following effects. > (1) Ignore zone watermark > (2) Don't call reclaim although allocation failure, instead return ENOMEM > (3) Don't invoke OOM Killer > (4) Don't retry internally in page alloc > > Some subsystem paid attention (1) only, and start to use PF_MEMALLOC abuse. > But, the fact is, PF_MEMALLOC is the promise of "I have lots freeable memory. > if I allocate few memory, I can return more much meory to the system!". > Non MM subsystem must not use PF_MEMALLOC. Memory reclaim > need few memory, anyone must not prevent it. Otherwise the system cause > mysterious hang-up and/or OOM Killer invokation. > > if many subsystem will be able to use emergency memory without any > usage rule, it isn't for emergency. it can become empty easily. > > Plus, characteristics (2)-(4) mean PF_MEMALLOC don't fit to general > high priority memory allocation. > > Thus, We kill all PF_MEMALLOC usage in no MM subsystem. >
I agree in principle with removing non-VM users of PF_MEMALLOC, but I think it should be left to the individual subsystem maintainers to apply or ack since the allocations may depend on the __GFP_NORETRY | ~__GFP_WAIT behavior of PF_MEMALLOC. This could be potentially dangerous for a PF_MEMALLOC user if allocations made by the kthread, for example, should never retry for orders smaller than PAGE_ALLOC_COSTLY_ORDER or block on direct reclaim.
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