RE: [External] Re: linux kernel page allocation failure and tuning of page cache

[Nagal, Amit UTC CCS]

-----Original Message-----
From: Matthew Wilcox [mailto:willy@xxxxxxxxxxxxx] 
Sent: Saturday, June 1, 2019 1:01 AM
To: Nagal, Amit UTC CCS <Amit.Nagal@xxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; CHAWLA, RITU UTC CCS <RITU.CHAWLA@xxxxxxx>; netdev@xxxxxxxxxxxxxxx
Subject: [External] Re: linux kernel page allocation failure and tuning of page cache

> 1) the platform is low memory platform having memory 64MB.
> 
> 2)  we are doing around 45MB TCP data transfer from PC to target using netcat utility .On Target , a process receives data over socket and writes the data to flash disk .

>I think your network is faster than your disk ...

Ok . I need to check it . But how does this affect page reclaim procedure .

> 5) sometimes , we observed kernel memory getting exhausted as page allocation failure happens in kernel  with the backtrace is printed below :
> # [  775.947949] nc.traditional: page allocation failure: order:0, 
> mode:0x2080020(GFP_ATOMIC)

>We're in the soft interrupt handler at this point, so we have very few options for freeing memory; we can't wait for I/O to complete, for example.

>That said, this is a TCP connection.  We could drop the packet silently without such a noisy warning.  Perhaps just collect statistics on how many packets we dropped due to a low memory situation.

I will collect statistics for it .

> [  775.956362] CPU: 0 PID: 1288 Comm: nc.traditional Tainted: G           O    4.9.123-pic6-g31a13de-dirty #19
> [  775.966085] Hardware name: Generic R7S72100 (Flattened Device Tree) 
> [  775.972501] [<c0109829>] (unwind_backtrace) from [<c010796f>] 
> (show_stack+0xb/0xc) [  775.980118] [<c010796f>] (show_stack) from 
> [<c0151de3>] (warn_alloc+0x89/0xba) [  775.987361] [<c0151de3>] 
> (warn_alloc) from [<c0152043>] (__alloc_pages_nodemask+0x1eb/0x634)
> [  775.995790] [<c0152043>] (__alloc_pages_nodemask) from [<c0152523>] 
> (__alloc_page_frag+0x39/0xde) [  776.004685] [<c0152523>] 
> (__alloc_page_frag) from [<c03190f1>] (__netdev_alloc_skb+0x51/0xb0) [  
> 776.013217] [<c03190f1>] (__netdev_alloc_skb) from [<c02c1b6f>] 
> (sh_eth_poll+0xbf/0x3c0) [  776.021342] [<c02c1b6f>] (sh_eth_poll) 
> from [<c031fd8f>] (net_rx_action+0x77/0x170) [  776.029051] 
> [<c031fd8f>] (net_rx_action) from [<c011238f>] 
> (__do_softirq+0x107/0x160) [  776.036896] [<c011238f>] (__do_softirq) 
> from [<c0112589>] (irq_exit+0x5d/0x80) [  776.044165] [<c0112589>] 
> (irq_exit) from [<c012f4db>] (__handle_domain_irq+0x57/0x8c) [  776.052007] [<c012f4db>] (__handle_domain_irq) from [<c01012e1>] (gic_handle_irq+0x31/0x48) [  776.060362] [<c01012e1>] (gic_handle_irq) from [<c0108025>] (__irq_svc+0x65/0xac) [  776.067835] Exception stack(0xc1cafd70 to 0xc1cafdb8)
> [  776.072876] fd60:                                     0002751c c1dec6a0 0000000c 521c3be5
> [  776.081042] fd80: 56feb08e f64823a6 ffb35f7b feab513d f9cb0643 
> 0000056c c1caff10 ffffe000 [  776.089204] fda0: b1f49160 c1cafdc4 
> c180c677 c0234ace 200e0033 ffffffff [  776.095816] [<c0108025>] 
> (__irq_svc) from [<c0234ace>] (__copy_to_user_std+0x7e/0x430) [  
> 776.103796] [<c0234ace>] (__copy_to_user_std) from [<c0241715>] 
> (copy_page_to_iter+0x105/0x250) [  776.112503] [<c0241715>] 
> (copy_page_to_iter) from [<c0319aeb>] 
> (skb_copy_datagram_iter+0xa3/0x108)
> [  776.121469] [<c0319aeb>] (skb_copy_datagram_iter) from [<c03443a7>] 
> (tcp_recvmsg+0x3ab/0x5f4) [  776.130045] [<c03443a7>] (tcp_recvmsg) 
> from [<c035e249>] (inet_recvmsg+0x21/0x2c) [  776.137576] [<c035e249>] 
> (inet_recvmsg) from [<c031009f>] (sock_read_iter+0x51/0x6e) [  
> 776.145384] [<c031009f>] (sock_read_iter) from [<c017795d>] 
> (__vfs_read+0x97/0xb0) [  776.152967] [<c017795d>] (__vfs_read) from 
> [<c01781d9>] (vfs_read+0x51/0xb0) [  776.159983] [<c01781d9>] 
> (vfs_read) from [<c0178aab>] (SyS_read+0x27/0x52) [  776.166837] [<c0178aab>] (SyS_read) from [<c0105261>] (ret_fast_syscall+0x1/0x54) [  776.174308] Mem-Info:
> [  776.176650] active_anon:2037 inactive_anon:23 isolated_anon:0 [  
> 776.176650]  active_file:2636 inactive_file:7391 isolated_file:32 [  
> 776.176650]  unevictable:0 dirty:1366 writeback:1281 unstable:0

>Almost all the dirty pages are under writeback at this point.

> [  776.176650]  slab_reclaimable:719 slab_unreclaimable:724 [  
> 776.176650]  mapped:1990 shmem:26 pagetables:159 bounce:0 [  
> 776.176650]  free:373 free_pcp:6 free_cma:0

>We have 373 free pages, but refused to allocate one of them to GFP_ATOMIC?
>I don't understand why that failed.  We also didn't try to steal an inactive_file or inactive_anon page, which seems like an obvious thing we might want to do.

Yes that's where I am concerned . we do not have swap device so I am assuming perhaps inactive_anon pages are not stolen , but inactive_file pages could have been used . 

> [  776.209062] Node 0 active_anon:8148kB inactive_anon:92kB 
> active_file:10544kB inactive_file:29564kB unevictable:0kB 
> isolated(anon):0kB isolated(file):128kB mapped:7960kB dirty:5464kB 
> writeback:5124kB shmem:104kB writeback_tmp:0kB unstable:0kB 
> pages_scanned:0 all_unreclaimable? no [  776.233602] Normal 
> free:1492kB min:964kB low:1204kB high:1444kB active_anon:8148kB 
> inactive_anon:92kB active_file:10544kB inactive_file:29564kB 
> unevictable:0kB writepending:10588kB present:65536kB managed:59304kB 
> mlocked:0kB slab_reclaimable:2876kB slab_unreclaimable:2896kB 
> kernel_stack:1152kB pagetables:636kB bounce:0kB free_pcp:24kB 
> local_pcp:24kB free_cma:0kB [  776.265406] lowmem_reserve[]: 0 0 [  
> 776.268761] Normal: 7*4kB (H) 5*8kB (H) 7*16kB (H) 5*32kB (H) 6*64kB 
> (H) 2*128kB (H) 2*256kB (H) 0*512kB 0*1024kB 0*2048kB 0*4096kB = 
> 1492kB
> 10071 total pagecache pages
> [  776.284124] 0 pages in swap cache
> [  776.287446] Swap cache stats: add 0, delete 0, find 0/0 [  
> 776.292645] Free swap  = 0kB [  776.295532] Total swap = 0kB [  
> 776.298421] 16384 pages RAM [  776.301224] 0 pages HighMem/MovableOnly 
> [  776.305052] 1558 pages reserved