Re: [PATCH v3 5/5] mm/slub: do not create dma-kmalloc if no managed pages in DMA zone
From: Hyeonggon Yoo <hidden>
Date: 2021-12-13 13:43:33
Also in:
kexec, linux-mm, lkml
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.
quoted hunk ↗ jump to hunk
--- 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