linux-kernel - Re: [PATCH] uio: add UIO_MEM

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Date:   Thu, 16 Feb 2017 09:34:43 +0800
From:   Xiubo Li <lixiubo@...s.chinamobile.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     agrover@...hat.com, mchristi@...hat.com, namei.unix@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uio: add UIO_MEM_CUSTOM support


>> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
>> index fba021f..6ca0ae0 100644
>> --- a/drivers/uio/uio.c
>> +++ b/drivers/uio/uio.c
>> @@ -708,6 +708,8 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
>>   		case UIO_MEM_LOGICAL:
>>   		case UIO_MEM_VIRTUAL:
>>   			return uio_mmap_logical(vma);
>> +		case UIO_MEM_CUSTOM:
>> +			return 0;
> How does this help?
For example, the TCMU will use the map area as ISCSI commands & data ring
buffer(uio0 --> map0). Currently the TCMU will using the fixed small 
size map
area as the ring buffer, but this will be the bottleneck for high iops.

Without knowing how large it is enough, so the new scheme will use the fixed
small ring buffer area(about 64M ~ 128M) + dynamically "growing" ring buffer
area(about 1.5G).

The fixed small area will be using vmalloc() when initializing, and 
dynamically
"growing" area will must use kmalloc() for some reasons.

...

> Can you provide an update to the documentation in
> Documentation/driver-api/uio-howto.rst to show how to use this?
Yes, I will update this.

Thanks.

BRs
Xiubo

> thanks,
>
> greg k-h