From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pf1-x436.google.com ([2607:f8b0:4864:20::436]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mwlc1-009lth-LO for kexec@lists.infradead.org; Mon, 13 Dec 2021 13:43:31 +0000 Received: by mail-pf1-x436.google.com with SMTP id k26so14943190pfp.10 for ; Mon, 13 Dec 2021 05:43:28 -0800 (PST) Date: Mon, 13 Dec 2021 13:43:19 +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: <20211213134319.GA997240@odroid> References: <20211213122712.23805-1-bhe@redhat.com> <20211213122712.23805-6-bhe@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211213122712.23805-6-bhe@redhat.com> 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: Baoquan He Cc: 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 , Vlastimil Babka Hello Baoquan. I have a question on your code. On Mon, Dec 13, 2021 at 08:27:12PM +0800, Baoquan He wrote: > Dma-kmalloc will be created as long as CONFIG_ZONE_DMA is enabled. > However, it will fail if DMA zone has no managed pages. The failure > can be seen in kdump kernel of x86_64 as below: > > CPU: 0 PID: 65 Comm: kworker/u2:1 Not tainted 5.14.0-rc2+ #9 > Hardware name: Intel Corporation SandyBridge Platform/To be filled by O.E.M., BIOS RMLSDP.86I.R2.28.D690.1306271008 06/27/2013 > Workqueue: events_unbound async_run_entry_fn > Call Trace: > dump_stack_lvl+0x57/0x72 > warn_alloc.cold+0x72/0xd6 > __alloc_pages_slowpath.constprop.0+0xf56/0xf70 > __alloc_pages+0x23b/0x2b0 > allocate_slab+0x406/0x630 > ___slab_alloc+0x4b1/0x7e0 > ? sr_probe+0x200/0x600 > ? lock_acquire+0xc4/0x2e0 > ? fs_reclaim_acquire+0x4d/0xe0 > ? lock_is_held_type+0xa7/0x120 > ? sr_probe+0x200/0x600 > ? __slab_alloc+0x67/0x90 > __slab_alloc+0x67/0x90 > ? sr_probe+0x200/0x600 > ? sr_probe+0x200/0x600 > kmem_cache_alloc_trace+0x259/0x270 > sr_probe+0x200/0x600 > ...... > bus_probe_device+0x9f/0xb0 > device_add+0x3d2/0x970 > ...... > __scsi_add_device+0xea/0x100 > ata_scsi_scan_host+0x97/0x1d0 > async_run_entry_fn+0x30/0x130 > process_one_work+0x2b0/0x5c0 > worker_thread+0x55/0x3c0 > ? process_one_work+0x5c0/0x5c0 > kthread+0x149/0x170 > ? set_kthread_struct+0x40/0x40 > ret_from_fork+0x22/0x30 > Mem-Info: > ...... > > The above failure happened when calling kmalloc() to allocate buffer with > GFP_DMA. It requests to allocate slab page from DMA zone while no managed > pages in there. > sr_probe() > --> get_capabilities() > --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA); > > The DMA zone should be checked if it has managed pages, then try to create > dma-kmalloc. > What is problem here? The slab allocator requested buddy allocator with GFP_DMA, and then buddy allocator failed to allocate page in DMA zone because there was no page in DMA zone. and then the buddy allocator called warn_alloc because it failed at allocating page. Looking at warn, I don't understand what the problem is. > --- > mm/slab_common.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index e5d080a93009..ae4ef0f8903a 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -878,6 +878,9 @@ void __init create_kmalloc_caches(slab_flags_t flags) > { > int i; > enum kmalloc_cache_type type; > +#ifdef CONFIG_ZONE_DMA > + bool managed_dma; > +#endif > > /* > * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined > @@ -905,10 +908,16 @@ void __init create_kmalloc_caches(slab_flags_t flags) > slab_state = UP; > > #ifdef CONFIG_ZONE_DMA > + managed_dma = has_managed_dma(); > + > for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) { > struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i]; > > if (s) { > + if (!managed_dma) { > + kmalloc_caches[KMALLOC_DMA][i] = kmalloc_caches[KMALLOC_NORMAL][i]; > + continue; > + } This code is copying normal kmalloc caches to DMA kmalloc caches. With this code, the kmalloc() with GFP_DMA will succeed even if allocated memory is not actually from DMA zone. Is that really what you want? Maybe the function get_capabilities() want to allocate memory even if it's not from DMA zone, but other callers will not expect that. Thanks, Hyeonggon. > 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