As per the documentation( https://elixir.bootlin.com/linux/latest/source/include/linux/gfp.h#L292), which says: #define GFP_KERNEL <https://elixir.bootlin.com/linux/latest/C/ident/GFP_KERNEL> (__GFP_RECLAIM <https://elixir.bootlin.com/linux/latest/C/ident/__GFP_RECLAIM> | __GFP_IO <https://elixir.bootlin.com/linux/latest/C/ident/__GFP_IO> | __GFP_FS <https://elixir.bootlin.com/linux/latest/C/ident/__GFP_FS>). It does not explicitly bind the option of *GFP_KERNEL *to any of the physical address zone modifiers(i.e. __GFP_DMA,__GFP_HIGHMEM,__GFP_DMA32,__GFP_MOVABLE,GFP_ZONEMASK) indeed. And there are free blocks in "Node 0 DMA" indeed. For your convenience, the most related log is seen below: *[22041.387948] Node 0 DMA: 3*4kB (U) 3*8kB (U) 1*16kB (U) 1*32kB (U) 3*64kB (U) 0*128kB 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15892kB[22041.387990] Node 0 DMA32: 14912*4kB (UME) 13850*8kB (UME) 9325*16kB (UME) 5961*32kB (UME) 3622*64kB (UME) 2359*128kB (UME) 1128*256kB (UME) 524*512kB (M) 194*1024kB (UM) 0*2048kB 0*4096kB = 1799872kB[22041.388033] Node 0 Normal: 1643*4kB (UME) 71*8kB (UME) 47*16kB (UM) 35*32kB (M) 38*64kB (M) 1*128kB (M) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 11572kB * Here is the implementation of the function *kzalloc(*refer to https://elixir.bootlin.com/linux/latest/source/include/linux/slab.h#L667*)*: /** * kzalloc - allocate memory. The memory is set to zero. * @size: how many bytes of memory are required. * @flags: the type of memory to allocate (see kmalloc). */static inline void *kzalloc <https://elixir.bootlin.com/linux/latest/C/ident/kzalloc>(size_t <https://elixir.bootlin.com/linux/latest/C/ident/size_t> size, gfp_t <https://elixir.bootlin.com/linux/latest/C/ident/gfp_t> flags){ return kmalloc <https://elixir.bootlin.com/linux/latest/C/ident/kmalloc>(size, flags | __GFP_ZERO <https://elixir.bootlin.com/linux/latest/C/ident/__GFP_ZERO>);} So I wonder why the kernel did not use the memory block contained by "Node 0 DMA" while the argument of kzalloc() is "GFP_KERNEL". I heard a saying is that the Linux kernel "will" search the "normal zone" first, then the "DMA32 zone", and "DMA zone" while there is no "physical address zone modifier" is explicitly declared. I have googled it for a long time. But I still could understand why this occurs. I would be grateful to have some help with it. *Here is the whole log:* [22041.387673] HelloWorldExamp: page allocation failure: order:9, mode:0x60c0c0(GFP_KERNEL|__GFP_COMP|__GFP_ZERO), nodemask=(null) [22041.387678] HelloWorldExamp cpuset=/ mems_allowed=0 [22041.387690] CPU: 3 PID: 27737 Comm: HelloWorldExamp Not tainted 4.19.84-bros #5 [22041.387693] Hardware name: Advantech UNO-2372G-J021AE/UNO-2372G-J021AE, BIOS 5.6.5 09/04/2019 [22041.387695] I-pipe domain: Linux [22041.387697] Call Trace: [22041.387711] dump_stack+0x9e/0xc8 [22041.387718] warn_alloc+0x100/0x190 [22041.387725] __alloc_pages_slowpath+0xb93/0xbd0 [22041.387732] __alloc_pages_nodemask+0x26d/0x2b0 [22041.387739] alloc_pages_current+0x6a/0xe0 [22041.387744] kmalloc_order+0x18/0x40 [22041.387748] kmalloc_order_trace+0x24/0xb0 [22041.387754] __kmalloc+0x20e/0x230 [22041.387759] ? __vmalloc_node_range+0x171/0x250 [22041.387765] xnheap_init+0x87/0x200 [22041.387770] ? remove_process+0xc0/0xc0 [22041.387775] cobalt_umm_init+0x61/0xb0 [22041.387779] cobalt_process_attach+0x64/0x4c0 [22041.387784] ? snprintf+0x45/0x70 [22041.387790] ? security_capable+0x46/0x60 [22041.387794] bind_personality+0x5a/0x120 [22041.387798] cobalt_bind_core+0x27/0x60 [22041.387803] CoBaLt_bind+0x18a/0x1d0 [22041.387812] ? handle_head_syscall+0x3f0/0x3f0 [22041.387816] ipipe_syscall_hook+0x119/0x340 [22041.387822] __ipipe_notify_syscall+0xd3/0x190 [22041.387827] ? __x64_sys_rt_sigaction+0x7b/0xd0 [22041.387832] ipipe_handle_syscall+0x3e/0xc0 [22041.387837] do_syscall_64+0x3b/0x250 [22041.387842] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [22041.387847] RIP: 0033:0x7ff3d074e481 [22041.387852] Code: 89 c6 48 8b 05 10 6b 21 00 c7 04 24 00 00 00 a4 8b 38 85 ff 75 43 bb 00 00 00 10 c7 44 24 04 11 00 00 00 48 89 e7 89 d8 0f 05 <bf> 04 00 00 00 48 89 c3 e8 e2 e0 ff ff 8d 53 26 83 fa 26 0f 87 46 [22041.387855] RSP: 002b:00007ffc62caf210 EFLAGS: 00000246 ORIG_RAX: 0000000010000000 [22041.387860] RAX: ffffffffffffffda RBX: 0000000010000000 RCX: 00007ff3d074e481 [22041.387863] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffc62caf210 [22041.387865] RBP: 00007ff3d20a3780 R08: 00007ffc62caf160 R09: 0000000000000000 [22041.387868] R10: 0000000000000008 R11: 0000000000000246 R12: 00007ff3d0965b00 [22041.387870] R13: 0000000001104320 R14: 00007ff3d0965d40 R15: 0000000001104050 [22041.387876] Mem-Info: [22041.387885] active_anon:56054 inactive_anon:109301 isolated_anon:0 active_file:110190 inactive_file:91980 isolated_file:0 unevictable:9375 dirty:1 writeback:0 unstable:0 slab_reclaimable:22463 slab_unreclaimable:19122 mapped:101678 shmem:25642 pagetables:7663 bounce:0 free:456443 free_pcp:0 free_cma:0 [22041.387891] Node 0 active_anon:224216kB inactive_anon:437204kB active_file:440760kB inactive_file:367920kB unevictable:37500kB isolated(anon):0kB isolated(file):0kB mapped:406712kB dirty:4kB writeback:0kB shmem:102568kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no [22041.387893] Node 0 DMA free:15892kB min:32kB low:44kB high:56kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:15992kB managed:15892kB mlocked:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB [22041.387901] lowmem_reserve[]: 0 2804 3762 3762 [22041.387912] Node 0 DMA32 free:1798624kB min:5836kB low:8704kB high:11572kB active_anon:188040kB inactive_anon:219400kB active_file:184156kB inactive_file:346776kB unevictable:24900kB writepending:0kB present:3017476kB managed:2927216kB mlocked:24900kB kernel_stack:1712kB pagetables:7564kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB [22041.387920] lowmem_reserve[]: 0 0 958 958 [22041.387930] Node 0 Normal free:11256kB min:1992kB low:2972kB high:3952kB active_anon:36084kB inactive_anon:218100kB active_file:257220kB inactive_file:21148kB unevictable:12600kB writepending:4kB present:1048576kB managed:981268kB mlocked:12600kB kernel_stack:5280kB pagetables:23088kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB [22041.387938] lowmem_reserve[]: 0 0 0 0 [22041.387948] Node 0 DMA: 3*4kB (U) 3*8kB (U) 1*16kB (U) 1*32kB (U) 3*64kB (U) 0*128kB 1*256kB (U) 0*512kB 1*1024kB (U) 1*2048kB (M) 3*4096kB (M) = 15892kB [22041.387990] Node 0 DMA32: 14912*4kB (UME) 13850*8kB (UME) 9325*16kB (UME) 5961*32kB (UME) 3622*64kB (UME) 2359*128kB (UME) 1128*256kB (UME) 524*512kB (M) 194*1024kB (UM) 0*2048kB 0*4096kB = 1799872kB [22041.388033] Node 0 Normal: 1643*4kB (UME) 71*8kB (UME) 47*16kB (UM) 35*32kB (M) 38*64kB (M) 1*128kB (M) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 11572kB [22041.388071] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB [22041.388073] 232507 total pagecache pages [22041.388077] 7 pages in swap cache [22041.388079] Swap cache stats: add 1015, delete 1008, find 0/1 [22041.388081] Free swap = 995068kB [22041.388083] Total swap = 999420kB [22041.388086] 1020511 pages RAM [22041.388088] 0 pages HighMem/MovableOnly [22041.388090] 39417 pages reserved [22041.388092] 0 pages hwpoisoned