Changing location of disk/filesystem cache

[Mandeep Sandhu]

Hi All,

I have a newbie question on disk/filesystem caches, so please bear with me!
:)

* Is disk cache the same as filesystem cache? Or there's nothing like a
filesysten cache and all disk I/O, irrespective of what FS is being
accessed, is cached in a "disk cache"?

* Is this caching done at the VFS layer?

* Can the location of a disk cache be changed, i.e instead of caching it in
memory (main RAM) can it be made to cache the files in a specific device?

To give some idea on why I'm asking these questions, I'll explain my
problem a little here (I myself have only started working on it so I don't
have all the details worked out yet).

I'm working on a special device which sits across the PCIe bus and accesses
files (or it's data) and does some processing with it. It transmits this
data out via a special high-speed link to another device (thats some black
hole for me right now). The transmit speed is in the 300-400 Gbps range.
This device also a lot of local memory, which is ~ 80GB.The PCIe interface
however supports transfer speeds which are much lower, i.e in the 5-8 Gbps
range.

In order to reduce latency in transmitting this content, I was thinking if
there's a way to make the disk cache content available in this device's
local memory.

Instead of writing a custom module for that, I was wondering if there
already exists a way in the kernel where a cache device can be specified
and the kernel uses that to store the cached file content?

Any ideas on making the cached content available inside the device are
welcome! :)

Regards,
-mandeep
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