On Mon, Dec 21, 2015 at 03:26:27AM +0200, Laurent Pinchart wrote: > On Friday 18 December 2015 20:20:56 Robin Murphy wrote: > > On 18/12/15 18:55, Doug Anderson wrote: > > > 2. We still have the same problem that we're taking away all the > > > contiguous memory that other users may want. I've got a dwc2 USB > > > controller in my system and it needs to allocate bounce buffers for > > > its DMA. While looking at cat videos on Facebook and running a > > > program to simulate memory pressure (4 userspace programs each walking > > > through 350 Megs of memory over and over) I start seeing lots of order > > > 3 allocation failures in dwc2. It's true that the USB/network stack > > > is resilient against these allocation failures (other than spamming my > > > log), but performance will decrease. When I switch to WiFi I suddenly > > > start seeing "mwifiex_sdio mmc2:0001:1: single skb allocated fail, > > > drop pkt port=28 len=33024". Again, it's robust, but you're affecting > > > performance. > > > > > > I also tried using "4" instead of "MAX_ORDER" (as per Marek) so that > > > we don't try for > 64K chunks. This is might be a reasonable > > > compromise. My cat video test still reproduces "alloc 4194304 bytes: > > > 674318751 ns", but maybe ~700 ms is an OK? Of course, this still eats > > > all the large chunks of memory that everyone else would like to have. > > > > > > Oh, or how about this: we start allocating of order 4. Upon the first > > > failure we jump to order 1. AKA: if there's no memory pressure we're > > > golden. The moment we have the first bit of memory pressure we fold. > > > That's basically just a slight optimization on Marek's suggestion. I > > > still see 450 ms for an allocation, but that's not too bad. It can > > > still take away large chunks from other users, but maybe that's OK? > > > > That makes sense - there's really no benefit to be had from trying > > orders which don't correspond to our relevant IOMMU page sizes - I'm not > > sure off-hand how many contortions you'd have to go through to actually > > get at those from here, although it might be another argument in favour > > of moving the pgsize_bitmap into the iommu_domain as Will proposed some > > time ago. > > What's the status of that ? Do we just need a volunteer to do the job ?
The pgsize_bitmap per domain stuff? It got a bunch of Acks, but Joerg didn't like it :( http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/334729.html The idea being that you should be able to attach arbitrary devices to arbitrary domains, something that I still don't think works in practice. One way forward would be to do what dwmw2 suggested here: http://lists.infradead.org/pipermail/linux-arm-kernel/2015-April/335023.html by extending the page table code to iterate and therefore support all page sizes. At that point, the pgsize_bitmap can be removed, although we will run into similar issues expressing the minimum supported page size. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
