Re: [PATCH] mm/vmscan: Fix hard LOCKUP in function isolate_lru_folios

[liuye]

On 2024/8/23 上午10:04, liuye wrote:
> I'm sorry to bother you about that, but it looks like the following email send 7 days ago, 
> did not receive a response from you. Do you mind having a look at this 
> when you have a bit of free time please?
> 
>>>> Fixes: b2e18757f2c9 ("mm, vmscan: begin reclaiming pages on a per-node basis")
>>>
>>> Merged in 2016.
>>>
>>> Under what circumstances does it occur?  
>>
>> User processe are requesting a large amount of memory and keep page active.
>> Then a module continuously requests memory from ZONE_DMA32 area.
>> Memory reclaim will be triggered due to ZONE_DMA32 watermark alarm reached.
>> However pages in the LRU(active_anon) list are mostly from 
>> the ZONE_NORMAL area.
>>
>>> Can you please describe how to reproduce this?  
>>
>> Terminal 1: Construct to continuously increase pages active(anon). 
>> mkdir /tmp/memory
>> mount -t tmpfs -o size=1024000M tmpfs /tmp/memory
>> dd if=/dev/zero of=/tmp/memory/block bs=4M
>> tail /tmp/memory/block
>>
>> Terminal 2:
>> vmstat -a 1
>> active will increase.
>> procs -----------memory---------- ---swap-- -----io---- -system-- -------cpu-------
>>  r  b   swpd   free  inact active   si   so    bi    bo   in   cs us sy id wa st gu
>>  1  0      0 1445623076 45898836 83646008    0    0     0     0 1807 1682  0  0 100  0  0  0
>>  1  0      0 1445623076 43450228 86094616    0    0     0     0 1677 1468  0  0 100  0  0  0
>>  1  0      0 1445623076 41003480 88541364    0    0     0     0 1985 2022  0  0 100  0  0  0
>>  1  0      0 1445623076 38557088 90987756    0    0     0     4 1731 1544  0  0 100  0  0  0
>>  1  0      0 1445623076 36109688 93435156    0    0     0     0 1755 1501  0  0 100  0  0  0
>>  1  0      0 1445619552 33663256 95881632    0    0     0     0 2015 1678  0  0 100  0  0  0
>>  1  0      0 1445619804 31217140 98327792    0    0     0     0 2058 2212  0  0 100  0  0  0
>>  1  0      0 1445619804 28769988 100774944    0    0     0     0 1729 1585  0  0 100  0  0  0
>>  1  0      0 1445619804 26322348 103222584    0    0     0     0 1774 1575  0  0 100  0  0  0
>>  1  0      0 1445619804 23875592 105669340    0    0     0     4 1738 1604  0  0 100  0  0  0
>>
>> cat /proc/meminfo | head
>> Active(anon) increase.
>> MemTotal:       1579941036 kB
>> MemFree:        1445618500 kB
>> MemAvailable:   1453013224 kB
>> Buffers:            6516 kB
>> Cached:         128653956 kB
>> SwapCached:            0 kB
>> Active:         118110812 kB
>> Inactive:       11436620 kB
>> Active(anon):   115345744 kB   
>> Inactive(anon):   945292 kB
>>
>> When the Active(anon) is 115345744 kB, insmod module triggers the ZONE_DMA32 watermark.
>>
>> perf show nr_scanned=28835844. 
>> 28835844 * 4k = 115343376KB approximately equal to 115345744 kB.
>>
>> perf record -e vmscan:mm_vmscan_lru_isolate -aR
>> perf script
>> isolate_mode=0 classzone=1 order=1 nr_requested=32 nr_scanned=2 nr_skipped=2 nr_taken=0 lru=active_anon
>> isolate_mode=0 classzone=1 order=1 nr_requested=32 nr_scanned=0 nr_skipped=0 nr_taken=0 lru=active_anon
>> isolate_mode=0 classzone=1 order=0 nr_requested=32 nr_scanned=28835844 nr_skipped=28835844 nr_taken=0 lru=active_anon
>> isolate_mode=0 classzone=1 order=1 nr_requested=32 nr_scanned=28835844 nr_skipped=28835844 nr_taken=0 lru=active_anon
>> isolate_mode=0 classzone=1 order=0 nr_requested=32 nr_scanned=29 nr_skipped=29 nr_taken=0 lru=active_anon
>> isolate_mode=0 classzone=1 order=0 nr_requested=32 nr_scanned=0 nr_skipped=0 nr_taken=0 lru=active_anon
>>
>> If increase Active(anon) to 1000G then insmod module triggers the ZONE_DMA32 watermark. hard lockup will occur.
>>
>> In my device nr_scanned = 0000000003e3e937 when hard lockup. Convert to memory size 0x0000000003e3e937 * 4KB = 261072092 KB.
>>
>> #5 [ffffc90006fb7c28] isolate_lru_folios at ffffffffa597df53
>>     ffffc90006fb7c30: 0000000000000020 0000000000000000 
>>     ffffc90006fb7c40: ffffc90006fb7d40 ffff88812cbd3000 
>>     ffffc90006fb7c50: ffffc90006fb7d30 0000000106fb7de8 
>>     ffffc90006fb7c60: ffffea04a2197008 ffffea0006ed4a48 
>>     ffffc90006fb7c70: 0000000000000000 0000000000000000 
>>     ffffc90006fb7c80: 0000000000000000 0000000000000000 
>>     ffffc90006fb7c90: 0000000000000000 0000000000000000 
>>     ffffc90006fb7ca0: 0000000000000000 0000000003e3e937 
>>     ffffc90006fb7cb0: 0000000000000000 0000000000000000 
>>     ffffc90006fb7cc0: 8d7c0b56b7874b00 ffff88812cbd3000 
>>
>>> Why do you think it took eight years to be discovered?
>>
>> The problem requires the following conditions to occur:
>> 1. The device memory should be large enough.
>> 2. Pages in the LRU(active_anon) list are mostly from the ZONE_NORMAL area.
>> 3. The memory in ZONE_DMA32 needs to reach the watermark.
>>
>> If the memory is not large enough, or if the usage design of ZONE_DMA32 area memory is reasonable, this problem is difficult to detect.
>>
>> notes:
>> The problem is most likely to occur in ZONE_DMA32 and ZONE_NORMAL, but other suitable scenarios may also trigger the problem.
>>
>>> It looks like that will fix, but perhaps something more fundamental
>>> needs to be done - we're doing a tremendous amount of pretty pointless
>>> work here.  Answers to my above questions will help us resolve this.
>>>
>>> Thanks.
>>
>> Please refer to the above explanation for details.
>>
>> Thanks.
> 
> Thanks.
> 
Friendly ping.