Messages in this thread | | | Date | Tue, 15 Oct 2019 02:55:22 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH] scatterlist: Validate page before calling PageSlab() |
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On Mon, Oct 07, 2019 at 02:13:51PM -0700, Alan Mikhak wrote: > > My goal is to not modify the Linux NVMe target code at all. The NVMe > > endpoint function driver currently does the work that is required.
You will have to do some modifications, as for example in PCIe you can have a n:1 relationship between SQs and CQs. And you need to handle the Create/Delete SQ/CQ commands, but not the fabrics commands. And modifying subsystems in Linux is perfectly acceptable, that is how they improve.
Do you have a pointer to your code?
> > In my current platform, there are no page struct backing for the PCIe > > memory address space.
In Linux there aren't struct pages for physical memory remapped using ioremap(). But if you want to feed them to the I/O subsystem you have to use devm_memremap_pages to create a page backing. Assuming you are on a RISC-V platform given your affiliation you'll need to ensure your kernel allows for ZONE_DEVICE pages, which Logan (added to Cc) has been working on. I don't remember what the current status is.
> Please consider the following information and cost estimate in > bytes for requiring page structs for PCI memory if used with > scatterlists. For example, a 128GB PCI memory address space > could require as much as 256MB of system memory just for > page struct backing. In a 1GB 64-bit system with flat memory > model, that consumes 25% of available memory. However, > not all of the 128GB PCI memory may be mapped for use at > a given time depending on the application. The cost of PCI > page structs is an upfront cost to be paid at system start.
I know the pages are costly. But once you want to feed them through subsystems that do expect pages you'll have to do that. And anything using scatterlists currently does. A little hack here and there isn't going to solve that.
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