Messages in this thread |  | | Date | Mon, 7 Apr 2008 14:15:56 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH] scsi: fix sense_slab/bio swapping livelock |
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On Tue, 8 Apr 2008, Pekka Enberg wrote: > > I wonder if we can get away with a SLAB_IO flag that you can use to annotate > caches that participate in writeout and the allocator could keep some spare > pages around that can be handed out for them in case of OOM...
Actually, I don't think this is SLAB-specific, since there are potentially the same issues for pages.
I suspect the right thing to do is not to mark them for "IO", but mark them for "short-lived", and allow short-lived allocations that don't have extended lifetimes to succeed even when a "real" allocation wouldn't.
When we are under memory pressure, a normal allocation generally needs to clear up enough memory from elsewhere to succeed. But a short-lived allocation without any long-term lifetimes would be known to release its memory back to the pool, so it can be allowed to go ahead when a normal memory allocation would not.
Examples of short-lived allocations: - IO requests - temporary network packets that don't get queued up (eg "ACK" packet) as opposed to those that do get queued (incoming _or_ outgoing queues) - things like the temporary buffers for "getname()/putname()" etc.
That said, even a lot of temporary allocations can at times have issues. If your IO layer is dead, your IO request queues that _should_ have been very temporary may end up staying around for a long time. But I do think that it makes sense to prioritize allocations that are known to be short- lived.
(It might also allows us to allocate them from different pools and just generally have other heuristics for cache behaviour - short-lived allocations simply have different behaviour)
Linus
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