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Date: Tue, 30 Jun 2026 18:01:17 +0300
From: Mike Rapoport <rppt@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>, Vlastimil Babka <vbabka@kernel.org>
Cc: Leon Romanovsky <leon@kernel.org>,
	Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-rdma@vger.kernel.org
Subject: Re: [PATCH 1/5] RDMA/umem: ib_umem_get(): use kmalloc() to allocate
 page array
Message-ID: <akPaPaCJdYINBEEV@kernel.org>
References: <20260630-b4-rdma-v1-0-ab42bcf0de92@kernel.org>
 <20260630-b4-rdma-v1-1-ab42bcf0de92@kernel.org>
 <20260630123150.GB7525@ziepe.ca>
 <akPaAp-0Zul8uVga@kernel.org>
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In-Reply-To: <akPaAp-0Zul8uVga@kernel.org>

(actually adding Vlastimil :) )

On Tue, Jun 30, 2026 at 06:00:24PM +0300, Mike Rapoport wrote:
> (adding Vlastimil)
> 
> On Tue, Jun 30, 2026 at 09:31:50AM -0300, Jason Gunthorpe wrote:
> > On Tue, Jun 30, 2026 at 01:52:29PM +0300, Mike Rapoport (Microsoft) wrote:
> > > ib_umem_get() allocates an array of pointers to struct page for
> > > pin_user_pages_fast() calls during memory registration.
> > 
> > A whole bunch of these use cases in rdma are really "give me some
> > temporary memory, I want it fast and as large as possible. In a
> > syscall context I will free it before returning back to userspace"
> 
> Not sure I follow where "as large as possible" comes from. Here it's
> explicitly a page.
> 
> And does "fast" mean that vmalloc() is not an option?
>  
> > eg we'd be really happy to get any kind of high order page here.
> > 
> > So, how would you feel about a new API?
> > 
> >  void *kmalloc_temporary(size_t min_size, size_t max_size, size_t *actual_size, gfp);
> > 
> > I know of a few other cases like this in the kernel at least.
> > 
> > The implementation could try to find an available high order page and
> > immediately return it, otherwise do a small reclaim allocation?
> 
> How do you suggest to decide how much of reclaim should happen? With the
> usual semantics of gfp?
> 
> > Jason
> 
> -- 
> Sincerely yours,
> Mike.

-- 
Sincerely yours,
Mike.