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 953907262E for ; Wed, 29 Jul 2026 21:45:31 +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=1785361534; cv=none; b=uUkQoc8ajtB4D60OvDjoa2tUGgGnaiFaWJwdEYqBAWwuvLgrzkxfcMfCzJaafhZuCOiZM8tyotUQyWb51SHqYMWrNZEv3980vtXC078D57Cpf5DCnZ0Ta7cxDF1N/1UWD5dRjnHm5v6wOmQPxXWHUdDsr58cQOmovHzIaK5kiIA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785361534; c=relaxed/simple; bh=x7L1/aO6HZ8KM4kPrfx1/hgoFUvWLrhbEpc+KkGP7sQ=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=dyMDrY4EmOfyDZ1O5EwfSxd5TO6HUEyGWbERJPN6M8vY1qQRY9e+zYdRC3egzX3xceQKhy9vd1HjCuqViHlR2XEFwW328IIF69qj/Rjx7ZRycHRpKDKJNUAxCG65LN2WN4Yh3cG/X/plVI6BriNWZVo/vnvJOBaKYoaG0Mkdoc4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=Xq4WBuMY; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="Xq4WBuMY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 733FC1F000E9; Wed, 29 Jul 2026 21:45:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785361529; bh=oDAZ9vi2KsO6qrLBZTAFU1nlDgmqJpzCkJDjK+DL7n4=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=Xq4WBuMYGkMr4QPhjIapmQ2FXmFaBhxTq6Uvu/arWojlSM2Kge4kTP5v7lG1ncA/M TNaJyESRoeFo+/uRbaFe2TBNtGfNVgiE/v24u3o7ycKwhIAGpFCkTFuRi2fjbGTGt1 orij7001+mUUXCUM8Pct4S37LBatIYD9rmNGnYoo= Date: Wed, 29 Jul 2026 14:45:29 -0700 From: Andrew Morton To: Matthew Wilcox Cc: Artem Lytkin , linux-mm@kvack.org, urezki@gmail.com, shivamkalra98@zohomail.in, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/vmalloc: make vm_struct.nr_pages an unsigned long Message-Id: <20260729144529.e1f1e0c7525954d23ab6a051@linux-foundation.org> In-Reply-To: References: <20260729175708.7074-1-iprintercanon@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 29 Jul 2026 19:28:36 +0100 Matthew Wilcox wrote: > On Wed, Jul 29, 2026 at 08:57:08PM +0300, Artem Lytkin wrote: > > A vmalloc area can hold more than 2^32 pages, but the page counts > > I had a "wait, what, really?" moment. And it can! 2^32 pages is 16TiB, > and x86-64 says: > > ffffc90000000000 | -55 TB | ffffe8ffffffffff | 32 TB | vmalloc/ioremap space (vmalloc_base) > > So we can have _one_ allocation that is more than 2^32 pages. But I'm > not sure where we'll get the memory to populate it from. > https://blogs.oracle.com/cloud-infrastructure/announcing-oci-compute-e6-acceleron-instances > says I can get 2.3TB of memory in a single machine, which is a factor of > 8 away from where we'd need to be to actually hit this. > > Intel are adveertising a max memory of 1.5TiB on the 6990E+ (128GiB * > 12 channels). So if you put 8 Xeons in a box and loaded it up, that > could get you to 12TiB. > > I'm not saying we shouldn't fix this, but it's all theoretical for now, > right? Artem said "That has produced the same truncation bug twice already, once in vread_iter() and once in the vrealloc() grow-in-place check". This might imply that the issue has been hit in practice, unclear. Anyway, it's a good change so let's do it. Sashiko wasn't able to apply it, and the mechanical checking would be useful here. I was able to get it to apply, took a bit of work. So Artem, can you please update the changelog to clarify the above, redo against mm.git's mm-new branch (or linux-next) and send us a v2?