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SubjectRe: [cma] 1ea6c22c9b: page_allocation_failure:order:#,mode:#(__GFP_RECLAIMABLE),nodemask=(null)
On Tue, 3 Nov 2020, kernel test robot wrote:

> Greeting,
>
> FYI, we noticed the following commit (built with gcc-9):
>
> commit: 1ea6c22c9b85ec176bb78d7076be06a4142f8bdd ("[PATCH 1/2] cma: redirect page allocation to CMA")
> url: https://github.com/0day-ci/linux/commits/Chris-Goldsworthy/Increasing-CMA-Utilization-with-a-GFP-Flag/20201102-224143
> base: https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git for-next
>
> in testcase: boot
>
> on test machine: qemu-system-i386 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
>
> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>
>
> +---------------------------------------------------------------------------+------------+------------+
> | | 67b6d2ce11 | 1ea6c22c9b |
> +---------------------------------------------------------------------------+------------+------------+
> | boot_successes | 6 | 0 |
> | boot_failures | 0 | 8 |
> | page_allocation_failure:order:#,mode:#(__GFP_RECLAIMABLE),nodemask=(null) | 0 | 8 |
> | Mem-Info | 0 | 8 |
> | kernel_BUG_at_kernel/workqueue.c | 0 | 8 |
> | invalid_opcode:#[##] | 0 | 8 |
> | EIP:workqueue_init_early | 0 | 8 |
> | Kernel_panic-not_syncing:Fatal_exception | 0 | 8 |
> +---------------------------------------------------------------------------+------------+------------+
>
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <rong.a.chen@intel.com>
>
>
> [ 2.108390] Memory: 8203240K/8388088K available (12819K kernel code, 6610K rwdata, 11292K rodata, 628K init, 12064K bss, 184848K reserved, 0K cma-reserved, 7481224K highmem)
> [ 2.111999] Checking if this processor honours the WP bit even in supervisor mode...Ok.
> [ 2.113918] random: get_random_u32 called from kmem_cache_open+0x1f/0x240 with crng_init=0
> [ 2.114387] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> [ 2.117656] Kernel/User page tables isolation: enabled
> [ 2.119610] swapper: page allocation failure: order:0, mode:0x10(__GFP_RECLAIMABLE), nodemask=(null)
> [ 2.121604] CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc1-00365-g1ea6c22c9b85 #1
> [ 2.123401] Call Trace:
> [ 2.123990] dump_stack+0x1b/0x1d
> [ 2.124787] warn_alloc+0x81/0xd9
> [ 2.125599] __alloc_pages_slowpath+0x79c/0x7a9
> [ 2.126690] ? get_page_from_freelist+0xb8/0x20d
> [ 2.127750] __alloc_pages_nodemask+0x107/0x188
> [ 2.128795] __alloc_pages_node+0x17/0x1c
> [ 2.129757] alloc_slab_page+0x26/0x4e
> [ 2.130649] allocate_slab+0x80/0x27e
> [ 2.131521] ___slab_alloc+0x247/0x2ec
> [ 2.132605] ? radix_tree_node_alloc+0x5e/0x8e
> [ 2.133915] ? validate_chain+0x5a8/0x5c3
> [ 2.134838] __slab_alloc+0x34/0x4d
> [ 2.135830] ? __slab_alloc+0x34/0x4d
> [ 2.136909] ? fs_reclaim_release+0x8/0x13
> [ 2.137910] kmem_cache_alloc+0x46/0x157
> [ 2.138854] ? radix_tree_node_alloc+0x5e/0x8e
> [ 2.140103] radix_tree_node_alloc+0x5e/0x8e
> [ 2.141369] idr_get_free+0xc1/0x21a
> [ 2.142230] idr_alloc_u32+0x4d/0x80
> [ 2.143016] idr_alloc+0x30/0x3e
> [ 2.143751] worker_pool_assign_id+0x37/0x47
> [ 2.144682] workqueue_init_early+0x9f/0x1f6
> [ 2.145707] start_kernel+0x206/0x467
> [ 2.146592] ? early_idt_handler_common+0x44/0x44
> [ 2.147671] i386_start_kernel+0x42/0x44
> [ 2.148607] startup_32_smp+0x164/0x168
> [ 2.149567] Mem-Info:
> [ 2.150101] active_anon:0 inactive_anon:0 isolated_anon:0
> [ 2.150101] active_file:0 inactive_file:0 isolated_file:0
> [ 2.150101] unevictable:0 dirty:0 writeback:0
> [ 2.150101] slab_reclaimable:0 slab_unreclaimable:88
> [ 2.150101] mapped:0 shmem:0 pagetables:0 bounce:0
> [ 2.150101] free:2050715 free_pcp:0 free_cma:0
> [ 2.156588] Node 0 active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB mapped:0kB dirty:0kB writeback:0kB shmem:0kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB kernel_stack:0kB all_unreclaimable? no
> [ 2.162313] Normal free:721636kB min:0kB low:0kB high:0kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:906864kB managed:722016kB mlocked:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> [ 2.162318] lowmem_reserve[]: 0 0 0
> [ 2.169009] HighMem free:7481224kB min:0kB low:0kB high:0kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:7481224kB managed:7481224kB mlocked:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> [ 2.169014] lowmem_reserve[]: 0 0 0
> [ 2.175914] Normal: 1*4kB (M) 2*8kB (M) 1*16kB (U) 2*32kB (UM) 2*64kB (M) 2*128kB (UM) 1*256kB (M) 0*512kB 2*1024kB (UM) 1*2048kB (M) 175*4096kB (M) = 721636kB
> [ 2.179229] HighMem: 0*4kB 1*8kB (M) 0*16kB 0*32kB 0*64kB 1*128kB (M) 1*256kB (M) 1*512kB (M) 1*1024kB (M) 2*2048kB (M) 1825*4096kB (M) = 7481224kB
> [ 2.182343] 0 total pagecache pages
> [ 2.183068] 2097022 pages RAM
> [ 2.183799] 1870306 pages HighMem/MovableOnly
> [ 2.184853] 46212 pages reserved
> [ 2.185675] 0 pages cma reserved

Normally what would happen for a __GFP_RECLAIMABLE allocation is that we'd
grab one of the free order-10 MIGRATE_MOVABLE pageblocks and convert it to
MIGRATE_RECLAIMABLE as fallback and then allocate the page from there.
Looks like the commit is breaking the fallback logic since I see an
abundance of free memory yet no MIGRATE_RECLAIMABLE pageblocks (which
would show 'E' in these lines):

Normal: 1*4kB (M) 2*8kB (M) 1*16kB (U) 2*32kB (UM) 2*64kB (M) 2*128kB (UM) 1*256kB (M) 0*512kB 2*1024kB (UM) 1*2048kB (M) 175*4096kB (M) = 721636kB
HighMem: 0*4kB 1*8kB (M) 0*16kB 0*32kB 0*64kB 1*128kB (M) 1*256kB (M) 1*512kB (M) 1*1024kB (M) 2*2048kB (M) 1825*4096kB (M) = 7481224kB

I'm concerned about the change in general, however, because it seems like
__GFP_CMA doesn't absolutely *have* to exist and we get code like this
that will quickly become unmaintainable:

#ifdef CONFIG_CMA
#define ___GFP_CMA 0x800000u
#else
#define ___GFP_CMA 0
#endif
#ifdef CONFIG_LOCKDEP
#ifdef CONFIG_CMA
#define ___GFP_NOLOCKDEP 0x1000000u
#else
#define ___GFP_NOLOCKDEP 0x800000u
#endif

I suspect that Michal Hocko <mhocko@suse.com> may also have an opinion on
this patch.

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