linux-kernel - Re: [PATCH v2 2/2] iommu/iova: Free global iova rcache on iova alloc failure

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Date:   Fri, 18 Sep 2020 15:41:00 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     vjitta@...eaurora.org, joro@...tes.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Cc:     vinmenon@...eaurora.org, kernel-team@...roid.com
Subject: Re: [PATCH v2 2/2] iommu/iova: Free global iova rcache on iova alloc
 failure

On 2020-08-20 13:49, vjitta@...eaurora.org wrote:
> From: Vijayanand Jitta <vjitta@...eaurora.org>
> 
> 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.
> 
> Signed-off-by: Vijayanand Jitta <vjitta@...eaurora.org>
> ---
>   drivers/iommu/iova.c | 23 +++++++++++++++++++++++
>   include/linux/iova.h |  6 ++++++
>   2 files changed, 29 insertions(+)
> 
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 4e77116..5836c87 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -442,6 +442,7 @@ struct iova *find_iova(struct iova_domain *iovad, unsigned long pfn)
>   		flush_rcache = false;
>   		for_each_online_cpu(cpu)
>   			free_cpu_cached_iovas(cpu, iovad);
> +		free_global_cached_iovas(iovad);
>   		goto retry;
>   	}
>   
> @@ -1055,5 +1056,27 @@ void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad)
>   	}
>   }
>   
> +/*
> + * free all the IOVA ranges of global cache
> + */
> +void free_global_cached_iovas(struct iova_domain *iovad)

As John pointed out last time, this should be static and the header 
changes dropped.

(TBH we should probably register our own hotplug notifier instance for a 
flush queue, so that external code has no need to poke at the per-CPU 
caches either)

Robin.

> +{
> +	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@...el.com>");
>   MODULE_LICENSE("GPL");
> diff --git a/include/linux/iova.h b/include/linux/iova.h
> index a0637ab..a905726 100644
> --- a/include/linux/iova.h
> +++ b/include/linux/iova.h
> @@ -163,6 +163,7 @@ int init_iova_flush_queue(struct iova_domain *iovad,
>   struct iova *split_and_remove_iova(struct iova_domain *iovad,
>   	struct iova *iova, unsigned long pfn_lo, unsigned long pfn_hi);
>   void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad);
> +void free_global_cached_iovas(struct iova_domain *iovad);
>   #else
>   static inline int iova_cache_get(void)
>   {
> @@ -270,6 +271,11 @@ static inline void free_cpu_cached_iovas(unsigned int cpu,
>   					 struct iova_domain *iovad)
>   {
>   }
> +
> +static inline void free_global_cached_iovas(struct iova_domain *iovad)
> +{
> +}
> +
>   #endif
>   
>   #endif
>