Re: Ang: Re: [Stgt-devel] Re: stgt a new version of iscsi target?

[Vladislav Bolkhovitin <vst@vlnb.net>]

FUJITA Tomonori wrote:
> From: Vladislav Bolkhovitin <vst@vlnb.net>
> Subject: Re: Ang: Re: [Stgt-devel] Re: [Iscsitarget-devel] stgt a new version of iscsi target?
> Date: Fri, 09 Dec 2005 18:28:58 +0300
> 
> 
>>>Also is the page cache comment in reference to us using the page cache 
>>>for our reads and writes or I am not sure why you wrote that if you do 
>>>not do it right now.
>>
>>Hm, at first, the page cache already used somehow in fileio dev handler 
>>(though, with additional mem copy). At the second, fully utilize the 
>>page cache is one of two major improvements that are pending in scst, 
>>because it is required changing the kernel, which until some moment try 
>>to avoid. Although I prepared what is necessary for that.
>>
>>The idea basically is the following. When READ operation arrives, pages 
>>for all requested blocks are at first searched in the page cache 
>>(probably, in SIRQ context, because it isn't expensive operation) and if 
>>all pages are found, they are referenced and the result will be sent to 
>>the initiator. Then the pages will be dereferenced (so, no pages 
>>allocation will be done at all). Otherwise, the missed pages will be 
>>allocated and the command will be rescheduled to the thread, which will 
>>read them. Then, after the response is sent, the pages will remain in 
>>the page cache for future accesses. For WRITEs the processing is the 
>>similar, the pages with the data will be put in the page cache.
> 
> The Ardis iSCSI target code does the same thing.

Perfectly. So, why don't do it on the mid-layer level where all targets 
can benefit from it?

Vlad


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