From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 1C2641AAA1E; Thu, 10 Apr 2025 16:52:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744303925; cv=none; b=sbydFO1yOEXoiIJBJtRqdFsHI+qd5uAZ3A0LrgH0GpT/8OtjQDka+bIMGB7ZoWh1QSbNtQOKUlO9nluLqJas2CHbzuIN+jXW2EulLWOuSzBW4IBEFRlTSli12bcL7szcUauv2TWP6s4cm0WCCo2c2pC/1k98zPYv0vKLlTq4Vq8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744303925; c=relaxed/simple; bh=h+pmHy2x2qcqGwPMErMQ2GPwatDQxp3usz35PZILRBo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HSWSXFtQ64OBtBMzJScRwvoM1PFQb9C+mLP23hoiCRYRSaMQqLj07NK4vdy4qCYmXZe7hClrtPQWuKH/LysPrJ3WLQfLcQQ1uW4n0pU2fN7rDt52cwtdAeg/5vlSD0u4+HVOiVhnmDmYdqNqmD2LjwgAbJteCLHM++mVuOblFgQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=RAnFP+sa; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="RAnFP+sa" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=EjNA9E6fQoObQrEF9x/xR2bwcpg2cboOt/4jyue8tog=; b=RAnFP+sa8REHwREQhuJs2YHIWN OrZAs12oMxeWbpncHVB29giNb8cyVPFV3+HdAb/cmklF4kTJD8BRqCv4exsJXSKaiW7dMlbUE2hHr 6rgi9NFwGz8ahECnVaFqrUK7nZu6YDFwiK+BHj3w1GQ+CEtykNrITzBxkTj4pqJiUfipuZUkHryYk FcoRDUUy751+rhrtNHwqavdxk62n4fXInDOnrKxh3cYuCP8m6EB01JqmoKvbOfJc3bUcP58GoemOM 1W4ZmB951GNXPtbhO0Bcpxn93wdKB00fjmkCjI9efyEMQ5M5eQvjPtqEsh9cRwdCtzr+Y2WqmmMYv c2UMaN8A==; Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1u2v83-000000039mo-2MIy; Thu, 10 Apr 2025 16:51:51 +0000 Date: Thu, 10 Apr 2025 17:51:51 +0100 From: Matthew Wilcox To: Jason Gunthorpe Cc: Mike Rapoport , Pratyush Yadav , Changyuan Lyu , linux-kernel@vger.kernel.org, graf@amazon.com, akpm@linux-foundation.org, luto@kernel.org, anthony.yznaga@oracle.com, arnd@arndb.de, ashish.kalra@amd.com, benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com, dave.hansen@linux.intel.com, dwmw2@infradead.org, ebiederm@xmission.com, mingo@redhat.com, jgowans@amazon.com, corbet@lwn.net, krzk@kernel.org, mark.rutland@arm.com, pbonzini@redhat.com, pasha.tatashin@soleen.com, hpa@zytor.com, peterz@infradead.org, robh+dt@kernel.org, robh@kernel.org, saravanak@google.com, skinsburskii@linux.microsoft.com, rostedt@goodmis.org, tglx@linutronix.de, thomas.lendacky@amd.com, usama.arif@bytedance.com, will@kernel.org, devicetree@vger.kernel.org, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Subject: Re: [PATCH v5 09/16] kexec: enable KHO support for memory preservation Message-ID: References: <20250407141626.GB1557073@nvidia.com> <20250407170305.GI1557073@nvidia.com> <20250409125630.GI1778492@nvidia.com> <20250409153714.GK1778492@nvidia.com> <20250409162837.GN1778492@nvidia.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250409162837.GN1778492@nvidia.com> On Wed, Apr 09, 2025 at 01:28:37PM -0300, Jason Gunthorpe wrote: > On Wed, Apr 09, 2025 at 07:19:30PM +0300, Mike Rapoport wrote: > > But we have memdesc today, it's struct page. > > No, I don't think it is. struct page seems to be turning into > something legacy that indicates the code has not been converted to the > new stuff yet. No, struct page will be with us for a while. Possibly forever. I have started reluctantly talking about a future in which there aren't struct pages, but it's really premature at this point. That's a 2030 kind of future. For 2025-2029, we will still have alloc_page(s)(). It's just that the size of struct page will be gradually shrinking over that time. > > And when the data structure that memdesc points to will be allocated > > separately folios won't make sense for order-0 allocations. > > At that point the lowest level allocator function will be allocating > the memdesc along with the struct page. Then folio will become > restricted to only actual folio memdescs and alot of the type punning > should go away. We are not there yet. We'll have a few allocator functions. There'll be a slab_alloc(), folio_alloc(), pt_alloc() and so on. I sketched out how these might work last year: https://kernelnewbies.org/MatthewWilcox/FolioAlloc > > > The lowest allocator primitive returns folios, which can represent any > > > order, and the caller casts to their own memdesc. > > > > The lowest allocation primitive returns pages. > > Yes, but as I understand things, we should not be calling that > interface in new code because we are trying to make 'struct page' go > away. > > Instead you should use the folio interfaces and cast to your own > memdesc, or use an allocator interface that returns void * (ie slab) > and never touch the struct page area. > > AFAICT, and I just wrote one of these.. Casting is the best you can do today because I haven't provided a better interface yet. > > And I don't think folio will be a lowest primitive buddy returns anytime > > soon if ever. > > Maybe not internally, but driver facing, I think it should be true. > > Like I just completely purged all struct page from the iommu code: > > https://lore.kernel.org/linux-iommu/0-v4-c8663abbb606+3f7-iommu_pages_jgg@nvidia.com/ > > I don't want some weird KHO interface that doesn't align with using > __folio_alloc_node() and folio_put() as the lowest level allocator > interface. I think it's fine to say "the KHO interface doesn't support bare pages; you must have a memdesc". But I'm not sure that's the right approach.