hi Michal:

> I would just mark NR_FREE_PAGES before and after allocation request.
> Something like:
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f8f3bfc435ee..a1337aa7e897 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3565,6 +3565,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>         enum compact_result compact_result;
>         int compaction_retries = 0;
>         int no_progress_loops = 0;
> +       unsigned long nr_free_before;
> +
> +       nr_free_before = global_page_state(NR_FREE_PAGES);
>
>         /*
>          * In the slowpath, we sanity check order to avoid ever trying to
> @@ -3624,6 +3627,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>                  * to fail.
>                  */
>                 WARN_ON_ONCE(gfp_mask & __GFP_NOFAIL);
> +               pr_info("nr_free_before:%lu nr_free_now:%lu\n", nr_free_before, global_page_state(NR_FREE_PAGES));
>                 goto nopage;
>         }
>
> You can then compare the numbers before after and the allocation failure
> to see whether there is a large gap.
I follow your suggestion to add nr_free_before for comparing when
allocation failure comes out.
from the log, it shows that nr_free_before has lot of free pages and
the value is the same even allocation fail.

It seems there are some other conditions that will let page order =0
with GFP_ATOMIC (mode = 0x20) fail even free pages and pcp is enough.

Sincerely appreciate your kind help,

nr_free_before:14094 nr_free_now:14094
opera_omi: page allocation failure: order:0, mode:0x20
CPU: 0 PID: 20846 Comm: opera_omi Tainted: G           O 3.10.0+ #14
Backtrace:
[<c00129f8>] (dump_backtrace+0x0/0x114) from [<c0012c68>] (show_stack+0x20/0x24)
 r6:ca01e000 r5:00000000 r4:00000020 r3:271ae71c
[<c0012c48>] (show_stack+0x0/0x24) from [<c056d32c>] (dump_stack+0x24/0x28)
[<c056d308>] (dump_stack+0x0/0x28) from [<c010c668>]
(warn_alloc_failed+0xec/0x128)
[<c010c57c>] (warn_alloc_failed+0x0/0x128) from [<c010fd58>]
(__alloc_pages_nodemask+0x748/0x97c)
 r3:00000000 r2:00000000
 r7:c07fe240 r6:00000000 r5:00000000 r4:00000020
[<c010f610>] (__alloc_pages_nodemask+0x0/0x97c) from [<c043ec04>]
(__netdev_alloc_frag+0x1cc/0x1e8)
[<c043ea38>] (__netdev_alloc_frag+0x0/0x1e8) from [<c04412cc>]
(__netdev_alloc_skb+0x84/0xe0)
[<c0441248>] (__netdev_alloc_skb+0x0/0xe0) from [<bfbf834c>]
(_rtw_skb_alloc+0x3c/0x40 [8812au])
 r6:0000007a r5:d4899168 r4:000000b6 r3:00000100
[<bfbf8310>] (_rtw_skb_alloc+0x0/0x40 [8812au]) from [<bfc0bc80>]
(rtw_os_alloc_recvframe+0x6c/0xfc [8812au])
[<bfc0bc14>] (rtw_os_alloc_recvframe+0x0/0xfc [8812au]) from
[<bfc4ea2c>] (recvbuf2recvframe+0x234/0x388 [8812au])
[<bfc4e7f8>] (recvbuf2recvframe+0x0/0x388 [8812au]) from [<bfbff438>]
(usb_recv_tasklet+0x6c/0x94 [8812au])
[<bfbff3cc>] (usb_recv_tasklet+0x0/0x94 [8812au]) from [<c002de24>]
(tasklet_action+0xa8/0x178)
 r7:c07b25ec r6:00000000 r5:d4809b5c r4:d4809b58
[<c002dd7c>] (tasklet_action+0x0/0x178) from [<c002cdd0>]
(__do_softirq+0x164/0x344)
 r8:cd919484 r7:00000018 r6:c07b8098 r5:ca01e000 r4:00000006
r3:c002dd7c
[<c002cc6c>] (__do_softirq+0x0/0x344) from [<c002d530>] (irq_exit+0xbc/0xf0)
[<c002d474>] (irq_exit+0x0/0xf0) from [<c000eda0>] (handle_IRQ+0x54/0xa0)
 r5:00000056 r4:c07b3f40
[<c000ed4c>] (handle_IRQ+0x0/0xa0) from [<c0008594>] (gic_handle_irq+0x3c/0x6c)
 r6:ca01fa00 r5:c07c82cc r4:feffe10c r3:00000000
[<c0008558>] (gic_handle_irq+0x0/0x6c) from [<c0571744>] (__irq_svc+0x44/0x78)
Exception stack(0xca01fa00 to 0xca01fa48)
fa00: cd919484 00000000 deaf1eed 80000001 cd919484 ca01fac0 00003175 00000000
fa20: cd919484 00000000 0000000c ca01fa5c ca01fa60 ca01fa48 c0570e0c c0294ee8
fa40: 880f0153 ffffffff 00000000
 r7:ca01fa34 r6:ffffffff r5:880f0153 r4:c0294ee8
[<c0294eb4>] (do_raw_read_lock+0x0/0x54) from [<c0570e0c>]
(_raw_read_lock+0x28/0x2c)
 r4:cd919484 r3:00000000
[<c0570de4>] (_raw_read_lock+0x0/0x2c) from [<c01f0940>]
(ext4_es_lookup_extent+0x30/0x1dc)
 r4:cd9192c8 r3:00000000
[<c01f0910>] (ext4_es_lookup_extent+0x0/0x1dc) from [<c01b5b18>]
(ext4_map_blocks+0x40/0x4cc)
 r8:00000000 r7:00000000 r6:cd9192c8 r5:00000000 r4:ca01fb18
r3:00000000
[<c01b5ad8>] (ext4_map_blocks+0x0/0x4cc) from [<c01b6038>]
(_ext4_get_block+0x94/0x188)
[<c01b5fa4>] (_ext4_get_block+0x0/0x188) from [<c01b6160>]
(ext4_get_block+0x34/0x3c)
 r9:00000000 r8:ca01fc40 r7:00000000 r6:00003175 r5:00000001
r4:00000000
[<c01b612c>] (ext4_get_block+0x0/0x3c) from [<c01873e8>]
(do_mpage_readpage+0x5ac/0x748)
[<c0186e3c>] (do_mpage_readpage+0x0/0x748) from [<c0187660>]
(mpage_readpages+0xdc/0x138)
[<c0187584>] (mpage_readpages+0x0/0x138) from [<c01b531c>]
(ext4_readpages+0x50/0x54)
[<c01b52cc>] (ext4_readpages+0x0/0x54) from [<c0113628>]
(__do_page_cache_readahead+0x1ac/0x260)
 r6:0000369a r5:00000020 r4:c01b52cc r3:00000014
[<c011347c>] (__do_page_cache_readahead+0x0/0x260) from [<c0113d88>]
(ra_submit+0x38/0x40)
[<c0113d50>] (ra_submit+0x0/0x40) from [<c01097e8>] (filemap_fault+0x3e4/0x438)
[<c0109404>] (filemap_fault+0x0/0x438) from [<c012997c>] (__do_fault+0x80/0x5d4)
[<c01298fc>] (__do_fault+0x0/0x5d4) from [<c012cbe4>]
(handle_pte_fault+0x84/0x6b0)
[<c012cb60>] (handle_pte_fault+0x0/0x6b0) from [<c012d29c>]
(handle_mm_fault+0x8c/0xbc)
[<c012d210>] (handle_mm_fault+0x0/0xbc) from [<c057354c>]
(do_page_fault+0x310/0x428)
[<c057323c>] (do_page_fault+0x0/0x428) from [<c000840c>]
(do_DataAbort+0x48/0xac)
[<c00083c4>] (do_DataAbort+0x0/0xac) from [<c05718dc>] (__dabt_usr+0x3c/0x40)
Exception stack(0xca01ffb0 to 0xca01fff8)
ffa0:                                     599ccd49 b59735cc 000048c4 b5e3784c
ffc0: 019e6fc8 b5e24cb8 00100080 00000000 be539aec 0196fc00 be5399e0 019e6fc8
ffe0: 00020817 be5398a0 b3bd4765 b3cf394a 280f0170 ffffffff ff131313
 r8:be539aec r7:00000000 r6:ffffffff r5:280f0170 r4:b3cf394a
Mem-info:
Normal per-cpu:
CPU    0: hi:   90, btch:  15 usd:  11
CPU    1: hi:   90, btch:  15 usd:  21
HighMem per-cpu:
CPU    0: hi:   18, btch:   3 usd:   1
CPU    1: hi:   18, btch:   3 usd:   2
active_anon:54429 inactive_anon:1744 isolated_anon:0
 active_file:2226 inactive_file:3338 isolated_file:0
 unevictable:0 dirty:44 writeback:0 unstable:0
 free:14094 slab_reclaimable:1380 slab_unreclaimable:6532
 mapped:4755 shmem:1772 pagetables:1106 bounce:0
 free_cma:13863
Normal free:56088kB min:2000kB low:2500kB high:3000kB
active_anon:148332kB inactive_anon:6040kB active_file:1356kB
inactive_file:5240kB unevictable:0kB isolated(anon):0kB
isolated(file):0kB present:329728kB managed:250408kB mlocked:0kB
dirty:120kB writeback:0kB mapped:8108kB shmem:6136kB
slab_reclaimable:5520kB slab_unreclaimable:26128kB kernel_stack:2720kB
pagetables:4424kB unstable:0kB bounce:0kB free_cma:55452kB
writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 696 696
HighMem free:288kB min:128kB low:304kB high:480kB active_anon:69384kB
inactive_anon:936kB active_file:7548kB inactive_file:8112kB
unevictable:0kB isolated(anon):0kB isolated(file):0kB present:89088kB
managed:89088kB mlocked:0kB dirty:56kB writeback:0kB mapped:10912kB
shmem:952kB slab_reclaimable:0kB slab_unreclaimable:0kB
kernel_stack:0kB pagetables:0kB unstable:0kB bounce:0kB free_cma:0kB
writeback_tmp:0kB pages_scanned:11 all_unreclaimable? no
lowmem_reserve[]: 0 0 0
Normal: 2152*4kB (UEC) 2157*8kB (UEC) 1889*16kB (UEC) 0*32kB 0*64kB
0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 56088kB
HighMem: 10*4kB (R) 21*8kB (R) 1*16kB (R) 0*32kB 1*64kB (R) 0*128kB
0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 288kB
7360 total pagecache pages
0 pages in swap cache
Swap cache stats: add 0, delete 0, find 0/0
Free swap  = 0kB
Total swap = 0kB
RTL871X: rtw_os_alloc_recvframe:can not allocate memory for skb copy
RTL871X: pre_recv_entry()-274: alloc_skb() failed!