Hi Robin, On Thu, Jun 30, 2022 at 10:02:00AM +0100, Robin Murphy wrote: > On 2022-06-30 08:33, Feng Tang wrote: > > kmalloc will round up the request size to power of 2, and current > > iova_magazine's size is 1032 (1024+8) bytes, so each instance > > allocated will get 2048 bytes from kmalloc, causing around 1KB > > waste. > > > > And in some exstreme case, the memory wasted can trigger OOM as > > reported in 2019 on a crash kernel with 256 MB memory [1]. > > I don't think it really needs pointing out that excessive memory consumption > can cause OOM. Especially not in the particularly silly context of a system > with only 2MB of RAM per CPU - that's pretty much guaranteed to be doomed > one way or another. Yes, the 256MB for 128 CPU is kind of extreme, will remove this. > > [ 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 > > [ 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 fix. > > + * will be wasted. > > + */ > > +#define IOVA_MAG_SIZE 127 > > The change itself seems perfectly reasonable, though. > > Acked-by: Robin Murphy <robin.murphy@xxxxxxx> Thanks for the review! - Feng > > #define MAX_GLOBAL_MAGS 32 /* magazines per bin */ > > struct iova_magazine {
