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

[FUJITA Tomonori]

From: Vladislav Bolkhovitin <vst at 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.