From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pj1-x1036.google.com ([2607:f8b0:4864:20::1036]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mxOKG-00H4Bb-FI for kexec@lists.infradead.org; Wed, 15 Dec 2021 07:03:47 +0000 Received: by mail-pj1-x1036.google.com with SMTP id oa5-20020a17090b1bc500b001b0f8a5e6b7so2792046pjb.0 for ; Tue, 14 Dec 2021 23:03:43 -0800 (PST) Date: Wed, 15 Dec 2021 07:03:35 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> Subject: Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone Message-ID: <20211215070335.GA1165926@odroid> References: <20211213122712.23805-1-bhe@redhat.com> <20211213122712.23805-6-bhe@redhat.com> <20211213134319.GA997240@odroid> <20211214053253.GB2216@MiWiFi-R3L-srv> <20211215044818.GB1097530@odroid> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211215044818.GB1097530@odroid> 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: Vlastimil Babka Cc: Baoquan He , linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, hch@lst.de, cl@linux.com, John.p.donnelly@oracle.com, kexec@lists.infradead.org, stable@vger.kernel.org, Pekka Enberg , David Rientjes , Joonsoo Kim On Wed, Dec 15, 2021 at 04:48:26AM +0000, Hyeonggon Yoo wrote: > > Hello Baoquan and Vlastimil. > > I'm not sure allowing ZONE_DMA32 for kdump kernel is nice way to solve > this problem. Devices that requires ZONE_DMA is rare but we still > support them. > > If we allow ZONE_DMA32 for ZONE_DMA in kdump kernels, > the problem will be hard to find. > Sorry, I sometimes forget validating my english writing :( What I meant: I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem. Devices that requires ZONE_DMA memory is rare but we still support them. If we use ZONE_DMA32 memory instead of ZONE_DMA in kdump kernels, It will be hard to the problem when we use devices that can use only ZONE_DMA memory. > What about one of those?: > > 1) Do not call warn_alloc in page allocator if will always fail > to allocate ZONE_DMA pages. > > > 2) let's check all callers of kmalloc with GFP_DMA > if they really need GFP_DMA flag and replace those by DMA API or > just remove GFP_DMA from kmalloc() > > 3) Drop support for allocating DMA memory from slab allocator > (as Christoph Hellwig said) and convert them to use DMA32 (as Christoph Hellwig said) and convert them to use *DMA API* > and see what happens > > Thanks, > Hyeonggon. > > > >> > > >> Maybe the function get_capabilities() want to allocate memory > > >> even if it's not from DMA zone, but other callers will not expect that. > > > > > > Yeah, I have the same guess too for get_capabilities(), not sure about other > > > callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is > > > the right way to call people when the first name is the same. Correct me if > > > it's wrong), any buffer requested from kmalloc can be used by device driver. > > > Means device enforces getting memory inside addressing limit for those > > > DMA transferring buffer which is usually large, Megabytes level with > > > vmalloc() or alloc_pages(), but doesn't care about this kind of small > > > piece buffer memory allocated with kmalloc()? Just a guess, please tell > > > a counter example if anyone happens to know, it could be easy. > > > > > > > > >> > > >> > kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( > > >> > kmalloc_info[i].name[KMALLOC_DMA], > > >> > kmalloc_info[i].size, > > >> > -- > > >> > 2.17.2 > > >> > > > >> > > > >> > > > > > _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec