Hi John, On Thu, Jun 30, 2022 at 11:52:18AM +0100, John Garry wrote: > > > > > > > > > [ 4.319253] iommu: Adding device 0000:06:00.2 to group 5 > > > > > [ 4.325869] iommu: Adding device 0000:20:01.0 to group 15 > > > > > [ 4.332648] iommu: Adding device 0000:20:02.0 to group 16 > > > > > [ 4.338946] swapper/0 invoked oom-killer: > > > > > gfp_mask=0x6040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null), > > > > > order=0, oom_score_adj=0 > > > > > [ 4.350251] swapper/0 cpuset=/ mems_allowed=0 > > > > > [ 4.354618] CPU: 0 PID: 1 Comm: swapper/0 Not > > > > > tainted 4.19.57.mx64.282 #1 > > > > > [ 4.355612] Hardware name: Dell Inc. PowerEdge > > > > > R7425/08V001, BIOS 1.9.3 06/25/2019 > > > > > [ 4.355612] Call Trace: > > > > > [ 4.355612] dump_stack+0x46/0x5b > > > > > [ 4.355612] dump_header+0x6b/0x289 > > > > > [ 4.355612] out_of_memory+0x470/0x4c0 > > > > > [ 4.355612] __alloc_pages_nodemask+0x970/0x1030 > > > > > [ 4.355612] cache_grow_begin+0x7d/0x520 > > > > > [ 4.355612] fallback_alloc+0x148/0x200 > > > > > [ 4.355612] kmem_cache_alloc_trace+0xac/0x1f0 > > > > > [ 4.355612] init_iova_domain+0x112/0x170 > > Note for Feng Tang: This callchain does not exist anymore since we separated > out the rcache init from the IOVA domain init. Indeed, not so much memory is > wasted for unused rcaches now. Thanks for the info, I also planned to remove the callstack as Robin suggested. > My point really is that it would be nicer to see a modern callchain - but > don't read that as me saying that the change is this patch is bad. > > > > > > [ 4.355612] amd_iommu_domain_alloc+0x138/0x1a0 > > > > > [ 4.355612] iommu_group_get_for_dev+0xc4/0x1a0 > > > > > [ 4.355612] amd_iommu_add_device+0x13a/0x610 > > > > > [ 4.355612] add_iommu_group+0x20/0x30 > > > > > [ 4.355612] bus_for_each_dev+0x76/0xc0 > > > > > [ 4.355612] bus_set_iommu+0xb6/0xf0 > > > > > [ 4.355612] amd_iommu_init_api+0x112/0x132 > > > > > [ 4.355612] state_next+0xfb1/0x1165 > > > > > [ 4.355612] amd_iommu_init+0x1f/0x67 > > > > > [ 4.355612] pci_iommu_init+0x16/0x3f > > > > > ... > > > > > [ 4.670295] Unreclaimable slab info: > > > > > ... > > > > > [ 4.857565] kmalloc-2048 59164KB 59164KB > > > > > > > > > > Change IOVA_MAG_SIZE from 128 to 127 to make size of 'iova_magazine' > > > > > 1024 bytes so that no memory will be wasted. > > > > > > > > > > [1]. https://lkml.org/lkml/2019/8/12/266 > > > > > > > > > > Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx> > > > > > --- > > > > > drivers/iommu/iova.c | 7 ++++++- > > > > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > > > > > index db77aa675145b..27634ddd9b904 100644 > > > > > --- a/drivers/iommu/iova.c > > > > > +++ b/drivers/iommu/iova.c > > > > > @@ -614,7 +614,12 @@ EXPORT_SYMBOL_GPL(reserve_iova); > > > > > * dynamic size tuning described in the paper. > > > > > */ > > > > > -#define IOVA_MAG_SIZE 128 > > > > > +/* > > > > > + * As kmalloc's buffer size is fixed to power of 2, 127 is chosen to > > > > > + * assure size of 'iova_magzine' to be 1024 bytes, so that no memory > > > > > > > > Typo: iova_magazine > > > > > > > > > + * will be wasted. > > > > > + */ > > > > > +#define IOVA_MAG_SIZE 127 > > > > > > I do wonder if we will see some strange new behaviour since > > > IOVA_FQ_SIZE % IOVA_MAG_SIZE != 0 now... > > > > I doubt it - even if a flush queue does happen to be entirely full of > > equal-sized IOVAs, a CPU's loaded magazines also both being perfectly > > empty when it comes to dump a full fq seem further unlikely, so in > > practice I don't see this making any appreciable change to the > > likelihood of spilling back to the depot or not. In fact the smaller the > > magazines get, the less time would be spent flushing the depot back to > > the rbtree, where your interesting workload falls off the cliff and> > never catches back up with the fq timer, so at some point it might even > > improve (unless it's also already close to the point where smaller > > caches would bottleneck allocation)... might be interesting to > > experiment with a wider range of magazine sizes if you had the time and > > inclination. > > > > ok, what you are saying sounds reasonable. I just remember that when we > analyzed the longterm aging issue that we concluded that the FQ size and its > relation to the magazine size was a factor and this change makes me a little > worried about new issues. Better the devil you know and all that... > > Anyway, if I get some time I might do some testing to see if this change has > any influence. > > Another thought is if we need even store the size in the iova_magazine? mags > in the depot are always full. As such, we only need worry about mags loaded > in the cpu rcache and their sizes, so maybe we could have something like > this: > > struct iova_magazine { > - unsigned long size; > unsigned long pfns[IOVA_MAG_SIZE]; > }; > > @@ -631,6 +630,8 @@ struct iova_cpu_rcache { > spinlock_t lock; > struct iova_magazine *loaded; > struct iova_magazine *prev; > + int loaded_size; > + int prev_size; > }; > > I haven't tried to implement it though.. I have very few knowledge of iova, so you can chose what's the better solution. I just wanted to raise the problem and will be happy to see it solved :) Thanks, Feng > Thanks, > John
