From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B5ABF480973; Thu, 2 Jul 2026 12:46:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782996410; cv=none; b=INZpigLzDIZ0hFhj29YjvfPYGf404sfSLD5Bs3TfaCfTibrR+SmO7s3PUwKvfV5qBsSfI+9Y3hNqvJsz6aYAy/duxE74Jm8OTovmFjnrZiTN0LQkkeuvU4HaCO7Y56y1rl5YOFrKE21L4qKZWD8SXb/TRoIdwRUqRNU4EdZrONw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782996410; c=relaxed/simple; bh=dt+ca4CC+6slbYrjTN17nZhbRvQsr4mNEjOzoKY7wYA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Rv+2ljq50S9wwyuNEwg9MMIfBTPtD4nYqiAw7OVbNqZAEiKxyWQ75F1R4gpuxxhyRP+OdMwsXIqghR7dT/3mzr/BHcM3mgizZTBHY3EZrZH+4fvp3yvyV/jsjaUgZWx6OUv+3VvrrE5oE9+AJLtzUnUq5019AMq2Vwm0efND0YM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LDhfcnye; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LDhfcnye" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A58FE1F000E9; Thu, 2 Jul 2026 12:46:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782996409; bh=YkczrDiyWe96M5D+D9rvpnIW1BoRRZ8dX9nGHodou1E=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=LDhfcnyeRDlUzx2GOlYE+uPNU74rEaXtarIcjC/oR0PAz0peBrTI42X/LYZZmTFov L4Icx4fv83rn+cKZF/I+S9OIUWo2++VNbNyRidedfcghtka83ZkHpau7K/DL6V9g16 +osycqYePEWB5Awrj91xWMwOkri86wIW1GPyaJmS6GRsKsWy4LU0wxmwg/apLAj/TY xgHjkOazY16Ghnaud7gL2R19b5rZJapl7Hzv8fmEptDvJ+YlqCkUDDGbT2tX3cZgsa N+QlKUApeKkqGndAOve8JbPHcmaRZt02ajdZTl3nazuUdFQjLWBb/BOq3kv/6yAg2q jLyLXgR1E04zw== Message-ID: <9cc11eeb-372a-49fb-ba89-486333ac71c4@kernel.org> Date: Thu, 2 Jul 2026 14:46:46 +0200 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] RDMA/umem: ib_umem_get(): use kmalloc() to allocate page array Content-Language: en-US To: Jason Gunthorpe , Mike Rapoport Cc: Leon Romanovsky , Dennis Dalessandro , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-rdma@vger.kernel.org, Matthew Wilcox , Michal Hocko , "David Hildenbrand (Red Hat)" , Dave Chinner References: <20260630-b4-rdma-v1-0-ab42bcf0de92@kernel.org> <20260630-b4-rdma-v1-1-ab42bcf0de92@kernel.org> <20260630123150.GB7525@ziepe.ca> <20260630153638.GG7525@ziepe.ca> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/30/26 17:36, Jason Gunthorpe wrote: > On Tue, Jun 30, 2026 at 06:01:17PM +0300, Mike Rapoport wrote: >> (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. > > It is a page because that is "fast" > > There will be a calculation what the upper limit of memory is that > this algorithm can use. > >> > And does "fast" mean that vmalloc() is not an option? > > Yes. The trade off is you do fewer iterations of some loop if you have > a bigger temporary buffer. But if it takes longer to allocate than the loop > iterations then it doesn't help. > >> > > 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? > > Yeah, when all options are exhausted you do some allocation with the > usual GFP options. I think this should be discussed more broadly and not block this change. Instead of adding just kmalloc_temporary() we should look at the bigger picture where we have manual optimistic nowait attempts with smaller fallbacks. Willy's LSF/MM plenary touched on this, as well as recent threads with Dave Chinner [1] etc. With that said, I'm for example not sure if "_temporary()" is really the distinguishing characteristic for this to be part of the name. [1] https://lore.kernel.org/all/1f50ce04-20e6-46a0-9d8a-00a5f7a74967@suse.com/ > Jason