On Wed, Jan 28, 2026 at 01:13:46PM +0200, Leon Romanovsky wrote:

On Wed, Jan 28, 2026 at 11:45:58AM +0800, D. Wythe wrote:

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On Tue, Jan 27, 2026 at 03:34:17PM +0200, Leon Romanovsky wrote:

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On Sat, Jan 24, 2026 at 10:57:54PM +0800, D. Wythe wrote:

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On Sat, Jan 24, 2026 at 11:48:59AM +0100, Uladzislau Rezki wrote:

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Hello, D. Wythe!

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On Fri, Jan 23, 2026 at 07:55:17PM +0100, Uladzislau Rezki wrote:

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On Fri, Jan 23, 2026 at 04:23:48PM +0800, D. Wythe wrote:

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find_vm_area() provides a way to find the vm_struct associated with a
virtual address. Export this symbol to modules so that modularized
subsystems can perform lookups on vmalloc addresses.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
---
 mm/vmalloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ecbac900c35f..3eb9fe761c34 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c

@@ -3292,6 +3292,7 @@ struct vm_struct *find_vm_area(const void *addr)
 
 	return va->vm;
 }
+EXPORT_SYMBOL_GPL(find_vm_area);
 

This is internal. We can not just export it.

--
Uladzislau Rezki

Hi Uladzislau,

Thank you for the feedback. I agree that we should avoid exposing
internal implementation details like struct vm_struct to external
subsystems.

Following Christoph's suggestion, I'm planning to encapsulate the page
order lookup into a minimal helper instead:

unsigned int vmalloc_page_order(const void *addr){
	struct vm_struct *vm;
 	vm = find_vm_area(addr);
	return vm ? vm->page_order : 0;
}
EXPORT_SYMBOL_GPL(vmalloc_page_order);

Does this approach look reasonable to you? It would keep the vm_struct
layout private while satisfying the optimization needs of SMC.

Could you please clarify why you need info about page_order? I have not
looked at your second patch.

Thanks!

--
Uladzislau Rezki

Hi Uladzislau,

This stems from optimizing memory registration in SMC-R. To provide the
RDMA hardware with direct access to memory buffers, we must register
them with the NIC. During this process, the hardware generates one MTT
entry for each physically contiguous block. Since these hardware entries
are a finite and scarce resource, and SMC currently defaults to a 4KB
registration granularity, a single 2MB buffer consumes 512 entries. In
high-concurrency scenarios, this inefficiency quickly exhausts NIC
resources and becomes a major bottleneck for system scalability.

I believe this complexity can be avoided by using the RDMA MR pool API,
as other ULPs do, for example NVMe.

Thanks

Hi Leon,

Am I correct in assuming you are suggesting mr_pool to limit the number
of MRs as a way to cap MTTE consumption?

I don't see this a limit, but something that is considered standard
practice to reduce MTT consumption.

quoted

However, our goal is to maximize the total registered memory within
the MTTE limits rather than to cap it. In SMC-R, each connection
occupies a configurable, fixed-size registered buffer; consequently,
the more memory we can register, the more concurrent connections
we can support.

It is not cap, but more efficient use of existing resources.

Got it. While MRs pool might be more standard practice, but it doesn't
address our specific bottleneck. In fact, smc already has its own internal
MR reuse; our core issue remains reducing MTTE consumption by increasing the
registration granularity to maximize the memory size mapped per MTT entry.