linux-kernel - Re: [PATCH net-next 2/3] mm: vmalloc: export find_vm

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Message-ID: <20260124093505.GA98529@j66a10360.sqa.eu95>
Date: Sat, 24 Jan 2026 17:35:05 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com    >
To: Uladzislau Rezki <urezki@...il.com>
Cc: "D. Wythe" <alibuda@...ux.alibaba.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dust Li <dust.li@...ux.alibaba.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Sidraya Jayagond <sidraya@...ux.ibm.com>,
	Wenjia Zhang <wenjia@...ux.ibm.com>,
	Mahanta Jambigi <mjambigi@...ux.ibm.com>,
	Simon Horman <horms@...nel.org>, Tony Lu <tonylu@...ux.alibaba.com>,
	Wen Gu <guwen@...ux.alibaba.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-rdma@...r.kernel.org,
	linux-s390@...r.kernel.org, netdev@...r.kernel.org,
	oliver.yang@...ux.alibaba.com
Subject: Re: [PATCH net-next 2/3] mm: vmalloc: export find_vm_area()

On Fri, Jan 23, 2026 at 07:55:17PM +0100, Uladzislau Rezki wrote:
> On Fri, Jan 23, 2026 at 04:23:48PM +0800, D. Wythe wrote:
> > 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@...ux.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.

Thanks,
D. Wythe