From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pg1-x531.google.com ([2607:f8b0:4864:20::531]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mwmD8-00A0WS-C5 for kexec@lists.infradead.org; Mon, 13 Dec 2021 14:21:51 +0000 Received: by mail-pg1-x531.google.com with SMTP id 133so14684018pgc.12 for ; Mon, 13 Dec 2021 06:21:49 -0800 (PST) Date: Mon, 13 Dec 2021 14:21:42 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> Subject: Re: [PATCH RESEND v2 0/5] Avoid requesting page from DMA zone when no managed pages Message-ID: <20211213142142.GA999996@odroid> References: <20211207030750.30824-1-bhe@redhat.com> <20211209080540.GA3050@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Christoph Lameter Cc: Baoquan He , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, hch@lst.de, robin.murphy@arm.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, vbabka@suse.cz, m.szyprowski@samsung.com, John.p.donnelly@oracle.com, kexec@lists.infradead.org On Thu, Dec 09, 2021 at 01:59:58PM +0100, Christoph Lameter wrote: > On Thu, 9 Dec 2021, Baoquan He wrote: > > > > The slab allocators guarantee that all kmalloc allocations are DMA able > > > indepent of specifying ZONE_DMA/ZONE_DMA32 > > > > Here you mean we guarantee dma-kmalloc will be DMA able independent of > > specifying ZONE_DMA/DMA32, or the whole sla/ub allocator? > > All memory obtained via kmalloc --independent of "dma-alloc", ZONE_DMA > etc-- must be dmaable. > > > With my understanding, isn't the reasonable sequence zone DMA firstly if > > GFP_DMA, then zone DMA32, finaly zone NORMAL. At least, on x86_64, I > > believe device driver developer prefer to see this because most of time, > > zone DMA and zone DMA32 are both used for dma buffer allocation, if > > IOMMU is not enabled. However, memory got from zone NORMAL when required > > with GFP_DMA, and it succeeds, does it mean that the developer doesn't > > take the GFP_DMA flag seriously, just try to get buffer for allocation? > > ZONE_NORMAL is also used for DMA allocations. ZONE_DMA and ZONE_DMA32 are > only used if the physical range of memory supported by a device does not > include all of normal memory. > > > > The size of ZONE_DMA is traditionally depending on the platform. On some > > > it is 16MB, on some 1G and on some 4GB. ZONE32 is always 4GB and should > > > only be used if ZONE_DMA has already been used. > > > > As said at above, ia64 and riscv don't have ZONE_DMA at all, they just > > cover low 4G with ZONE_DMA32 alone. > > If you do not have devices that are crap and cannot address the full > memory then you dont need these special zones. > > Sorry this subject has caused confusion multiple times over the years and > there are still arches that are not implementing this in a consistent way. Hello Baoquan and Christoph. I'm the confused one here too. :) So the point is that ZONE_NORMAL is also dma-able if the device can access normal memory. (which is false for ISA devices, ancient PCI devices, ...etc.) Then if I understand right, I think the patch 5/5 (mm/slub: Avoid ...) should be removing GFP_DMA flag from the function sr_probe() -> get_capabilities, rather than copying copying normal kmalloc caches to dma kmalloc caches. (If the device does not have limitation in its address space.) Please let me know If I got it wrong :) Thanks, Hyeonggon. _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec