unevictable page

Question

I getting a kernel crash as below. Here I can observe large memory is present in unevictablle page. I wish to know when exactly memory is added to unevictable page list.

Also, from the below message I can understand only 1724kB is available in the system. is it correct?

kswapd0: page allocation failure. order:0, mode:0xd0
[<c002aed4>] (unwind_backtrace+0x0/0xdc) from [<c006d5b0>] (__alloc_pages_nodemask+0x490/0x4ec)
[<c006d5b0>] (__alloc_pages_nodemask+0x490/0x4ec) from [<c008416c>] (cache_alloc_refill+0x260/0x4f4)
[<c008416c>] (cache_alloc_refill+0x260/0x4f4) from [<c0084498>] (__kmalloc+0x98/0xd8)
[<c0084498>] (__kmalloc+0x98/0xd8) from [<c01f73d8>] (__alloc_skb+0x44/0x124)
[<c01f73d8>] (__alloc_skb+0x44/0x124) from [<c01f7cac>] (skb_copy+0x2c/0xa0)
Exception stack(0xc4ecbdf0 to 0xc4ecbe38)
bde0:                                     00000000 00000064 c0347718 00000000 
be00: 00000001 00000000 c0347718 c0347718 c4ecbf54 00000000 00000000 000000fd 
be20: c4ecbf00 c4ecbe38 c00724b4 c00724c4 80000013 ffffffff                   
[<c0024b18>] (__irq_svc+0x38/0xc0) from [<c00724c4>] (shrink_zone+0x88/0x70c)
[<c00724c4>] (shrink_zone+0x88/0x70c) from [<c0072ff4>] (kswapd+0x34c/0x4d8)
[<c0072ff4>] (kswapd+0x34c/0x4d8) from [<c004dcec>] (kthread+0x7c/0x84)
[<c004dcec>] (kthread+0x7c/0x84) from [<c0025ed0>] (kernel_thread_exit+0x0/0x8)
Mem-info:
Normal per-cpu:
CPU    0: hi:   42, btch:   7 usd:  36
Active_anon:124 active_file:0 inactive_anon:129
 inactive_file:0 unevictable:8111 dirty:0 writeback:0 unstable:0
 free:431 slab:19526 mapped:408 pagetables:53 bounce:0
Normal free:1724kB min:1396kB low:1744kB high:2092kB active_anon:496kB inactive_anon:516kB active_file:0kB inactive_file:0kB unevictable:32444kB present:121920kB pages_scanned:0 all_unreclaimable? no
lowmem_reserve[]: 0 0
Normal: 103*4kB 34*8kB 3*16kB 3*32kB 2*64kB 0*128kB 1*256kB 1*512kB 0*1024kB 0*2048kB 0*4096kB 0*8192kB 0*16384kB = 1724kB
8114 total pagecache pages
30720 pages of RAM
547 free pages
1204 reserved pages
19526 slab pages
1662 pages shared
0 pages swap cached

Answer 1

Unevictable pages are simply pages that can't be paged out for a variety of reasons. It might mean that the page belongs to a ramdisk, was protected by a call to mlock(), shared and locked, or any other circumstances where the kernel was told 'don't touch'. This is managed by the kernel's LRU framework.

Can you provide some more context into the crash?