Messages in this thread | | | Date | Thu, 30 Jun 2022 10:02:00 +0100 | Subject | Re: [PATCH] iommu/iova: change IOVA_MAG_SIZE to 127 to save memory | From | Robin Murphy <> |
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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.
> [ 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@intel.com> > --- > 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
The change itself seems perfectly reasonable, though.
Acked-by: Robin Murphy <robin.murphy@arm.com>
> #define MAX_GLOBAL_MAGS 32 /* magazines per bin */ > > struct iova_magazine {
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