On 08/13/2014 03:01 PM, Daniel Vetter wrote: > On Wed, Aug 13, 2014 at 02:35:52PM +0200, Thomas Hellstrom wrote: >> On 08/13/2014 12:42 PM, Daniel Vetter wrote: >>> On Wed, Aug 13, 2014 at 11:06:25AM +0200, Thomas Hellstrom wrote: >>>> On 08/13/2014 05:52 AM, Jérôme Glisse wrote: >>>>> From: Jérôme Glisse <jglisse@xxxxxxxxxx> >>>>> >>>>> When experiencing memory pressure we want to minimize pool size so that >>>>> memory we just shrinked is not added back again just as the next thing. >>>>> >>>>> This will divide by 2 the maximum pool size for each device each time >>>>> the pool have to shrink. The limit is bumped again is next allocation >>>>> happen after one second since the last shrink. The one second delay is >>>>> obviously an arbitrary choice. >>>> Jérôme, >>>> >>>> I don't like this patch. It adds extra complexity and its usefulness is >>>> highly questionable. >>>> There are a number of caches in the system, and if all of them added >>>> some sort of voluntary shrink heuristics like this, we'd end up with >>>> impossible-to-debug unpredictable performance issues. >>>> >>>> We should let the memory subsystem decide when to reclaim pages from >>>> caches and what caches to reclaim them from. >>> Yeah, artificially limiting your cache from growing when your shrinker >>> gets called will just break the equal-memory pressure the core mm uses to >>> rebalance between all caches when workload changes. In i915 we let >>> everything grow without artificial bounds and only rely upon the shrinker >>> callbacks to ensure we don't consume more than our fair share of available >>> memory overall. >>> -Daniel >> Now when you bring i915 memory usage up, Daniel, >> I can't refrain from bringing up the old user-space unreclaimable kernel >> memory issue, for which gem open is a good example ;) Each time >> user-space opens a gem handle, some un-reclaimable kernel memory is >> allocated, for which there is no accounting, so theoretically I think a >> user can bring a system to unusability this way. >> >> Typically there are various limits on unreclaimable objects like this, >> like open file descriptors, and IIRC the kernel even has an internal >> limit on the number of struct files you initialize, based on the >> available system memory, so dma-buf / prime should already have some >> sort of protection. > Oh yeah, we have zero cgroups limits or similar stuff for gem allocations, > so there's not really a way to isolate gpu memory usage in a sane way for > specific processes. But there's also zero limits on actual gpu usage > itself (timeslices or whatever) so I guess no one asked for this yet. In its simplest form (like in TTM if correctly implemented by drivers) this type of accounting stops non-privileged malicious GPU-users from exhausting all system physical memory causing grief for other kernel systems but not from causing grief for other GPU users. I think that's the minimum level that's intended also for example also for the struct file accounting. > My comment really was about balancing mm users under the assumption that > they're all unlimited. Yeah, sorry for stealing the thread. I usually bring this up now and again but nowadays with an exponential backoff. > -Daniel Thomas _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
