[PATCH 2/3] x86, swiotlb: Try coherent allocations with __GFP_NOWARN

[Joerg Roedel]

From: Joerg Roedel <jroedel@xxxxxxx>

When we boot a kdump kernel in high memory, there is by
default only 72MB of low memory available. The swiotlb code
takes 64MB of it (by default) so that there are only 8MB
left to allocate from. On systems with many devices this
causes page allocator warnings from dma_generic_alloc_coherent():

systemd-udevd: page allocation failure: order:0, mode:0x280d4
CPU: 0 PID: 197 Comm: systemd-udevd Tainted: G        W       3.12.28-4-default #1
Hardware name: HP ProLiant DL980 G7, BIOS P66 07/30/2012
 ffff8800781335e0 ffffffff8150b1db 00000000000280d4 ffffffff8113af90
 0000000000000000 0000000000000000 ffff88007efdbb00 0000000100000000
 0000000000000000 0000000000000000 0000000000000000 0000000000000001
Call Trace:
 [<ffffffff8100467d>] dump_trace+0x7d/0x2d0
 [<ffffffff81004964>] show_stack_log_lvl+0x94/0x170
 [<ffffffff81005d91>] show_stack+0x21/0x50
 [<ffffffff8150b1db>] dump_stack+0x41/0x51
 [<ffffffff8113af90>] warn_alloc_failed+0xf0/0x160
 [<ffffffff8150763a>] __alloc_pages_slowpath+0x72f/0x796
 [<ffffffff8113ee7a>] __alloc_pages_nodemask+0x1ea/0x210
 [<ffffffff81008256>] dma_generic_alloc_coherent+0x96/0x140
 [<ffffffff8103fccc>] x86_swiotlb_alloc_coherent+0x1c/0x50
 [<ffffffffa048ae5b>] ttm_dma_pool_alloc_new_pages+0xab/0x320 [ttm]
 [<ffffffffa048bc6e>] ttm_dma_populate+0x3ce/0x640 [ttm]
 [<ffffffffa0486>] ttm_tt_bind+0x36/0x60 [ttm]
 [<ffffffffa0484faf>] ttm_bo_handle_move_mem+0x55f/0x5c0 [ttm]
 [<ffffffffa0485be5>] ttm_bo_move_buffer+0x105/0x130 [ttm]
 [<ffffffffa0485cd1>] ttm_bo_validate+0xc1/0x130 [ttm]
 [<ffffffffa0485f8b>] ttm_bo_init+0x24b/0x400 [ttm]
 [<ffffffffa054f8bc>] radeon_bo_create+0x16c/0x200 [radeon]
 [<ffffffffa0563c8e>] radeon_ring_init+0x11e/0x2b0 [radeon]
 [<ffffffffa056c143>] r100_cp_init+0x123/0x5b0 [radeon]
 [<ffffffffa056e8e4>] r100_startup+0x194/0x230 [radeon]
 [<ffffffffa056ece3>] r100_init+0x223/0x410 [radeon]
 [<ffffffffa053495f>] radeon_device_init+0x6af/0x830 [radeon]
 [<ffffffffa0536979>] radeon_driver_load_kms+0x89/0x180 [radeon]
 [<ffffffffa04eeb31>] drm_get_pci_dev+0x121/0x2f0 [drm]
 [<ffffffff812d3ec9>ocal_pci_probe+0x39/0x60
 [<ffffffff812d51e9>] pci_device_probe+0xa9/0x120
 [<ffffffff8139871d>] driver_probe_device+0x9d/0x3d0
 [<ffffffff81398b1b>] __driver_attach+0x8b/0x90
 [<ffffffff8139667b>] bus_for_each_dev+0x5b/0x90
 [<ffffffff81397cd8>] bus_add_driver+0x1f8/0x2c0
 [<ffffffff8139911b>] driver_register+0x5b/0xe0
 [<ffffffff810002c2>] do_one_initcall+0xf2/0x1a0
 [<ffffffff810c8837>] load_module+0x1207/0x1c70
 [<ffffffff810c93f5>] SYSC_finit_module+0x75/0xa0
 [<ffffffff81519329>] system_call_fastpath+0x16/0x1b
 [<00007fac533d2789>] 0x7fac533d2788

After these warnings the code enters a fall-back path and
allocated directly from the swiotlb aperture in the end.
So remove these warnings as this is not a fatal error.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
 arch/x86/kernel/pci-swiotlb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
index 77dd0ad..79b2291 100644
--- a/arch/x86/kernel/pci-swiotlb.c
+++ b/arch/x86/kernel/pci-swiotlb.c
@@ -20,6 +20,14 @@ void *x86_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 {
 	void *vaddr;
 
+	/*
+	 * When booting a kdump kernel in high memory these allocations are very
+	 * likely to fail, as there are by default only 8MB of low memory to
+	 * allocate from. So disable the warnings from the allocator when this
+	 * happens.  SWIOTLB also implements fall-backs for failed allocations.
+	 */
+	flags |= __GFP_NOWARN;
+
 	vaddr = dma_generic_alloc_coherent(hwdev, size, dma_handle, flags,
 					   attrs);
 	if (vaddr)
-- 
1.9.1

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