From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 21 May 2008 13:30:32 +0200 From: Miquel van Smoorenburg Subject: 2.6.26: x86/kernel/pci_dma.c: gfp |= __GFP_NORETRY ? Message-ID: <20080521113028.GA24632@xs4all.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Glauber Costa List-ID: I've recently switched some of my boxes from a 32 to a 64 bit kernel. These are usenet server boxes that do a lot of I/O. They are running 2.6.24 / 2.6.25 Every 15 minutes a cronjob calls a management utility, tw_cli, to read the raid status of the 3ware disk arrays. That often fails with a segmentation violation .. tw_cli: page allocation failure. order:0, mode:0x10d0 Pid: 9296, comm: tw_cli Not tainted 2.6.25.4 #2 Call Trace: [] __alloc_pages+0x336/0x390 [] dma_alloc_pages+0x24/0xa0 [] dma_alloc_coherent+0xa3/0x2e0 [] :3w_9xxx:twa_chrdev_ioctl+0x11f/0x810 [] chrdev_open+0x0/0x1c0 [] __dentry_open+0x197/0x210 [] vfs_ioctl+0x7d/0xa0 [] do_vfs_ioctl+0x74/0x2d0 [] sys_ioctl+0x49/0x80 [] system_call_after_swapgs+0x7b/0x80 Mem-info: DMA per-cpu: CPU 0: hi: 0, btch: 1 usd: 0 CPU 1: hi: 0, btch: 1 usd: 0 CPU 2: hi: 0, btch: 1 usd: 0 CPU 3: hi: 0, btch: 1 usd: 0 DMA32 per-cpu: CPU 0: hi: 186, btch: 31 usd: 60 CPU 1: hi: 186, btch: 31 usd: 185 CPU 2: hi: 186, btch: 31 usd: 176 CPU 3: hi: 186, btch: 31 usd: 165 Normal per-cpu: CPU 0: hi: 186, btch: 31 usd: 120 CPU 1: hi: 186, btch: 31 usd: 164 CPU 2: hi: 186, btch: 31 usd: 177 CPU 3: hi: 186, btch: 31 usd: 182 Active:265929 inactive:1657355 dirty:663189 writeback:62890 unstable:0 free:49079 slab:65923 mapped:1238 pagetables:927 bounce:0 DMA free:12308kB min:184kB low:228kB high:276kB active:0kB inactive:0kB present:11816kB pages_scanned:0 all_unreclaimable? yes lowmem_reserve[]: 0 3255 8053 8053 DMA32 free:94200kB min:52912kB low:66140kB high:79368kB active:440616kB inactive:2505772kB present:3333792kB pages_scanned:0 all_unreclaimable? no lowmem_reserve[]: 0 0 4797 4797 Normal free:86792kB min:77968kB low:97460kB high:116952kB active:623100kB inactive:4126872kB present:4912640kB pages_scanned:32 all_unreclaimable? no lowmem_reserve[]: 0 0 0 0 DMA: 3*4kB 5*8kB 2*16kB 6*32kB 4*64kB 4*128kB 0*256kB 0*512kB 1*1024kB 1*2048kB 2*4096kB = 12308kB DMA32: 150*4kB 5*8kB 2299*16kB 120*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 13*4096kB = 94512kB Normal: 462*4kB 3803*8kB 123*16kB 24*32kB 2*64kB 1*128kB 1*256kB 1*512kB 0*1024kB 0*2048kB 18*4096kB = 109760kB 1653409 total pagecache pages Swap cache: add 5748, delete 5411, find 4317/4852 Free swap = 4588488kB Total swap = 4594580kB Free swap: 4588488kB 2293760 pages of RAM 249225 reserved pages 1658761 pages shared 337 pages swap cached (this is easily reproducible by pinning a lot of memory with mmap/mlock, say 6 GB on an 8 GB box, while running cat /dev/zero > filename, then invoking tw_cli) Now this appears to happen because dma_alloc_coherent() in pci-dma_64.c does this: /* Don't invoke OOM killer */ gfp |= __GFP_NORETRY; However, if you read mm/page_alloc.c you can see that this not only prevents invoking the OOM killer, it also does what it says: no retries when allocating memory. That means that dma_alloc_coherent(..., GFP_KERNEL) can become unreliable. Bad news. pci-dma_32 does not do this. And in 2.6.26-rc1, pci-dma_32.c and pci-dma_64.c were merged, so now the 32 bit kernel has the same problem. Does anyone know why this was added on x86_64 ? If not I think this patch should go into 2.6.26: diff -ruN linux-2.6.26-rc3.orig/arch/x86/kernel/pci-dma.c linux-2.6.26-rc3/arch/x86/kernel/pci-dma.c --- linux-2.6.26-rc3.orig/arch/x86/kernel/pci-dma.c 2008-05-18 23:36:41.000000000 +0200 +++ linux-2.6.26-rc3/arch/x86/kernel/pci-dma.c 2008-05-21 13:15:54.000000000 +0200 @@ -397,9 +397,6 @@ if (dev->dma_mask == NULL) return NULL; - /* Don't invoke OOM killer */ - gfp |= __GFP_NORETRY; - #ifdef CONFIG_X86_64 /* Why <=? Even when the mask is smaller than 4GB it is often larger than 16MB and in this case we have a chance of Ideas ? Maybe a __GFP_NO_OOMKILLER ? Mike. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org