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Date: Sat, 20 Jan 2007 01:56:43 +0300 From: Evgeniy Polyakov <johnpol@....mipt.ru> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, linux-mm@...ck.org, David Miller <davem@...emloft.net> Subject: Re: Possible ways of dealing with OOM conditions. On Fri, Jan 19, 2007 at 01:53:15PM +0100, Peter Zijlstra (a.p.zijlstra@...llo.nl) wrote: > > 2. You differentiate by hand between critical and non-critical > > allocations by specifying some kernel users as potentially possible to > > allocate from reserve. > > True, all sockets that are needed for swap, no-one else. > > > This does not prevent from NVIDIA module to > > allocate from that reserve too, does it? > > All users of the NVidiot crap deserve all the pain they get. > If it breaks they get to keep both pieces. I meant that pretty anyone can be those user, who can just add a bit into own gfp_flags which are used for allocation. > > And you artificially limit > > system to process only tiny bits of what it must do, thus potentially > > leaking pathes which must use reserve too. > > How so? I cover pretty much every allocation needed to process an skb by > setting PF_MEMALLOC - the only drawback there is that the reserve might > not actually be large enough because it covers more allocations that > were considered. (thats one of the TODO items, validate the reserve > functions parameters) You only covered ipv4/v6 and arp, maybe some route updates. But it is very possible, that some allocations are missed like multicast/broadcast. Selecting only special pathes out of the whole possible network alocations tends to create a situation, when something is missed or cross dependant on other pathes. > > So, solution is to have a reserve in advance, and manage it using > > special path when system is in OOM. So you will have network memory > > reserve, which will be used when system is in trouble. It is very > > similar to what you had. > > > > But the whole reserve can never be used at all, so it should be used, > > but not by those who can create OOM condition, thus it should be > > exported to, for example, network only, and when system is in trouble, > > network would be still functional (although only critical pathes). > > But the network can create OOM conditions for itself just fine. > > Consider the remote storage disappearing for a while (it got rebooted, > someone tripped over the wire etc..). Now the rest of the network > traffic keeps coming and will queue up - because user-space is stalled, > waiting for more memory - and we run out of memory. Hmm... Neither UDP, nor TCP work that way actually. > There must be a point where we start dropping packets that are not > critical to the survival of the machine. You still can drop them, the main point is that network allocations do not depend on other allocations. > > Even further development of such idea is to prevent such OOM condition > > at all - by starting swapping early (but wisely) and reduce memory > > usage. > > These just postpone execution but will not avoid it. No. If system allows to have such a condition, then something is broken. It must be prevented, instead of creating special hacks to recover from it. -- Evgeniy Polyakov - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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