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

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Date:   Tue, 3 Nov 2020 14:31:20 +0000
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, <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 v5 2/2] iommu/iova: Free global iova rcache on iova alloc
 failure

On 03/11/2020 12:35, Robin Murphy wrote:
> On 2020-09-30 08:44, 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.
> 

If we do clear all the CPU rcaches, it would nice to have something 
immediately available to replenish, i.e. use the global rcache, instead 
of flushing it, if that is not required...

> This looks reasonable to me - it's mildly annoying that we end up with 
> so many similar-looking functions,

Well I did add a function to clear all CPU rcaches here, if you would 
like to check:

https://lore.kernel.org/linux-iommu/1603733501-211004-2-git-send-email-john.garry@huawei.com/

> 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@....com>
> 
>> Signed-off-by: Vijayanand Jitta <vjitta@...eaurora.org>
>> ---
>>   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);

a thought: It would be great if the file could be rearranged at some 
point where we don't require so many forward declarations.

>>   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;

I don't think that NULLify is strictly necessary

>> +        }
>> +        rcache->depot_size = 0;
>> +        spin_unlock_irqrestore(&rcache->lock, flags);
>> +    }
>> +}
>>   MODULE_AUTHOR("Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>");
>>   MODULE_LICENSE("GPL");
>>
> _______________________________________________
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> iommu@...ts.linux-foundation.org
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