Re: [PATCH v5 2/2] iommu/iova: Free global iova rcache on iova alloc failure

[Robin Murphy]

On 2020-09-30 08:44, vjitta@xxxxxxxxxxxxxx wrote:
> From: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
>
> When ever an iova alloc request fails we free the iova
> ranges present in the percpu iova rcaches and then retry
> but the global iova rcache is not freed as a result we could
> still see iova alloc failure even after retry as global
> rcache is holding the iova's which can cause fragmentation.
> So, free the global iova rcache as well and then go for the
> retry.

This looks reasonable to me - it's mildly annoying that we end up with 
so many similar-looking functions, but the necessary differences are 
right down in the middle of the loops so nothing can reasonably be 
factored out :(

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

> Signed-off-by: Vijayanand Jitta <vjitta@xxxxxxxxxxxxxx>
> ---
>   drivers/iommu/iova.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index c3a1a8e..faf9b13 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -25,6 +25,7 @@ static void init_iova_rcaches(struct iova_domain *iovad);
>   static void free_iova_rcaches(struct iova_domain *iovad);
>   static void fq_destroy_all_entries(struct iova_domain *iovad);
>   static void fq_flush_timeout(struct timer_list *t);
> +static void free_global_cached_iovas(struct iova_domain *iovad);
>   
>   void
>   init_iova_domain(struct iova_domain *iovad, unsigned long granule,
> @@ -442,6 +443,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size,
>   		flush_rcache = false;
>   		for_each_online_cpu(cpu)
>   			free_cpu_cached_iovas(cpu, iovad);
> +		free_global_cached_iovas(iovad);
>   		goto retry;
>   	}
>   
> @@ -1057,5 +1059,26 @@ void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad)
>   	}
>   }
>   
> +/*
> + * free all the IOVA ranges of global cache
> + */
> +static void free_global_cached_iovas(struct iova_domain *iovad)
> +{
> +	struct iova_rcache *rcache;
> +	unsigned long flags;
> +	int i, j;
> +
> +	for (i = 0; i < IOVA_RANGE_CACHE_MAX_SIZE; ++i) {
> +		rcache = &iovad->rcaches[i];
> +		spin_lock_irqsave(&rcache->lock, flags);
> +		for (j = 0; j < rcache->depot_size; ++j) {
> +			iova_magazine_free_pfns(rcache->depot[j], iovad);
> +			iova_magazine_free(rcache->depot[j]);
> +			rcache->depot[j] = NULL;
> +		}
> +		rcache->depot_size = 0;
> +		spin_unlock_irqrestore(&rcache->lock, flags);
> +	}
> +}
>   MODULE_AUTHOR("Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>");
>   MODULE_LICENSE("GPL");