Messages in this thread | | | Date | Thu, 30 Jun 2022 10:37:25 +0100 | Subject | Re: [PATCH] iommu/iova: change IOVA_MAG_SIZE to 127 to save memory | From | John Garry <> |
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On 30/06/2022 10:02, 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. > >> [ 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
I do wonder if we will see some strange new behaviour since IOVA_FQ_SIZE % IOVA_MAG_SIZE != 0 now...
> > The change itself seems perfectly reasonable, though. > > Acked-by: Robin Murphy <robin.murphy@arm.com>
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