Mike Christie wrote:
Vladislav Bolkhovitin wrote:
FUJITA Tomonori wrote:
From: Vladislav Bolkhovitin <vst@xxxxxxxx>
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?
Any target can hook into stgt too? What is your point since neither of
us are in mainline or even close given the scsi guy's veiwpoint on where
to do reads and writes?
My point is to show one of the benefits of the kernel side
implementation. Any target driver (of scst or stgt, doesn't matter)
should benefit from it. Obviously, there is no point to overcomplicate
any target driver with the functions of the the mid-level.
Vlad
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