Hi Joonsoon,
I am currently working on STM32 microcontroller family upstream.
The STM32 family is ARM Cortex-M based, so no MMU.
As user-space, I use a ramdisk with a statically-linked busybox installed.
On v3.19, I am facing a memory leak.
Each time I run a command one page is lost. Here an example with
busybox's free command:
/ # free
total used free shared buffers cached
Mem: 7928 1972 5956 0 0 492
-/+ buffers/cache: 1480 6448
/ # free
total used free shared buffers cached
Mem: 7928 1976 5952 0 0 492
-/+ buffers/cache: 1484 6444
/ # free
total used free shared buffers cached
Mem: 7928 1980 5948 0 0 492
-/+ buffers/cache: 1488 6440
/ # free
total used free shared buffers cached
Mem: 7928 1984 5944 0 0 492
-/+ buffers/cache: 1492 6436
/ # free
total used free shared buffers cached
Mem: 7928 1988 5940 0 0 492
-/+ buffers/cache: 1496 6432
At some point, the system fails to sastisfy 256KB allocations:
[ 38.720000] free: page allocation failure: order:6, mode:0xd0
[ 38.730000] CPU: 0 PID: 67 Comm: free Not tainted
3.19.0-05389-gacf2cf1-dirty #64
[ 38.740000] Hardware name: STM32 (Device Tree Support)
[ 38.740000] [<08022e25>] (unwind_backtrace) from [<080221e7>]
(show_stack+0xb/0xc)
[ 38.750000] [<080221e7>] (show_stack) from [<0804fd3b>]
(warn_alloc_failed+0x97/0xbc)
[ 38.760000] [<0804fd3b>] (warn_alloc_failed) from [<08051171>]
(__alloc_pages_nodemask+0x295/0x35c)
[ 38.770000] [<08051171>] (__alloc_pages_nodemask) from [<08051243>]
(__get_free_pages+0xb/0x24)
[ 38.780000] [<08051243>] (__get_free_pages) from [<0805127f>]
(alloc_pages_exact+0x19/0x24)
[ 38.790000] [<0805127f>] (alloc_pages_exact) from [<0805bdbf>]
(do_mmap_pgoff+0x423/0x658)
[ 38.800000] [<0805bdbf>] (do_mmap_pgoff) from [<08056e73>]
(vm_mmap_pgoff+0x3f/0x4e)
[ 38.810000] [<08056e73>] (vm_mmap_pgoff) from [<08080949>]
(load_flat_file+0x20d/0x4f8)
[ 38.820000] [<08080949>] (load_flat_file) from [<08080dfb>]
(load_flat_binary+0x3f/0x26c)
[ 38.830000] [<08080dfb>] (load_flat_binary) from [<08063741>]
(search_binary_handler+0x51/0xe4)
[ 38.840000] [<08063741>] (search_binary_handler) from [<08063a45>]
(do_execveat_common+0x271/0x35c)
[ 38.850000] [<08063a45>] (do_execveat_common) from [<08063b49>]
(do_execve+0x19/0x1c)
[ 38.860000] [<08063b49>] (do_execve) from [<08020a01>]
(ret_fast_syscall+0x1/0x4a)
[ 38.870000] Mem-info:
[ 38.870000] Normal per-cpu:
[ 38.870000] CPU 0: hi: 0, btch: 1 usd: 0
[ 38.880000] active_anon:0 inactive_anon:0 isolated_anon:0
[ 38.880000] active_file:0 inactive_file:0 isolated_file:0
[ 38.880000] unevictable:123 dirty:0 writeback:0 unstable:0
[ 38.880000] free:1515 slab_reclaimable:17 slab_unreclaimable:139
[ 38.880000] mapped:0 shmem:0 pagetables:0 bounce:0
[ 38.880000] free_cma:0
[ 38.910000] Normal free:6060kB min:352kB low:440kB high:528kB
active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB
unevictable:492kB isolated(anon):0ks
[ 38.950000] lowmem_reserve[]: 0 0
[ 38.950000] Normal: 23*4kB (U) 22*8kB (U) 24*16kB (U) 23*32kB (U)
23*64kB (U) 23*128kB (U) 1*256kB (U) 0*512kB 0*1024kB 0*2048kB
0*4096kB = 6060kB
[ 38.970000] 123 total pagecache pages
[ 38.970000] 2048 pages of RAM
[ 38.980000] 1538 free pages
[ 38.980000] 66 reserved pages
[ 38.990000] 109 slab pages
[ 38.990000] -46 pages shared
[ 38.990000] 0 pages swap cached
[ 38.990000] nommu: Allocation of length 221184 from process 67 (free) failed
[ 39.000000] Normal per-cpu:
[ 39.010000] CPU 0: hi: 0, btch: 1 usd: 0
[ 39.010000] active_anon:0 inactive_anon:0 isolated_anon:0
[ 39.010000] active_file:0 inactive_file:0 isolated_file:0
[ 39.010000] unevictable:123 dirty:0 writeback:0 unstable:0
[ 39.010000] free:1515 slab_reclaimable:17 slab_unreclaimable:139
[ 39.010000] mapped:0 shmem:0 pagetables:0 bounce:0
[ 39.010000] free_cma:0
[ 39.050000] Normal free:6060kB min:352kB low:440kB high:528kB
active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB
unevictable:492kB isolated(anon):0ks
[ 39.090000] lowmem_reserve[]: 0 0
[ 39.090000] Normal: 23*4kB (U) 22*8kB (U) 24*16kB (U) 23*32kB (U)
23*64kB (U) 23*128kB (U) 1*256kB (U) 0*512kB 0*1024kB 0*2048kB
0*4096kB = 6060kB
[ 39.100000] 123 total pagecache pages
[ 39.110000] Unable to allocate RAM for process text/data, errno 12
SEGV
I found that this is a regression, which has been introduced with this patch:
------------------------------------------------------------------------------
commit dbc8358c72373daa4f37b7e233fecbc47105fe54
Author: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Date: Fri Dec 12 16:55:55 2014 -0800
mm/nommu: use alloc_pages_exact() rather than its own implementation
do_mmap_private() in nommu.c try to allocate physically contiguous pages
with arbitrary size in some cases and we now have good abstract function
to do exactly same thing, alloc_pages_exact(). So, change to use it.
There is no functional change. This is the preparation step for support
page owner feature accurately.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
------------------------------------------------------------------------------
Indeed, when I revert it, the issue no more appear, I can run the free
command for hours without any issue.
The problem is that I fail to understand what in your patch could
cause the issue.
I enabled the traces in mm/nommu.c file, this is what I get with you patch:
[ 5.970000] ==> do_mmap_pgoff(,0,36000,7,2,0)
[ 5.970000] xxxalloc order 6 for 36000yyy
[ 5.970000] xxxtry to alloc exact 54 pagesyyy
[ 5.970000] ==> add_vma_to_mm(,d0781600)
[ 5.970000] <== do_mmap_pgoff() = d0540000
[ 5.990000] ==> do_mmap_pgoff(,0,2000,3,4000021,0)
[ 5.990000] xxxalloc order 1 for 2000yyy
[ 5.990000] ==> add_vma_to_mm(,d07818a0)
[ 5.990000] <== do_mmap_pgoff() = d0576000
[ 6.000000] ==> exit_mmap()
[ 6.000000] ==> delete_vma_from_mm(d0781600)
[ 6.000000] ==> delete_vma(d0781600)
[ 6.000000] ==> __put_nommu_region(d078f120{1})
[ 6.000000] xxxfree seriesyyy
[ 6.000000] xxx- free d0540000yyy
[ 6.000000] xxx- free d0541000yyy
[ 6.010000] xxx- free d0542000yyy
</snip>
[ 6.020000] xxx- free d0572000yyy
[ 6.020000] xxx- free d0573000yyy
[ 6.020000] xxx- free d0574000yyy
[ 6.020000] xxx- free d0575000yyy
[ 6.020000] ==> delete_vma_from_mm(d07818a0)
[ 6.020000] ==> delete_vma(d07818a0)
[ 6.020000] ==> __put_nommu_region(d078f0f0{1})
[ 6.020000] xxxfree seriesyyy
[ 6.020000] xxx- free d0576000yyy
[ 6.020000] xxx- free d0577000yyy
[ 6.020000] xxxfree page d07faee0: refcount not one: 0yyy
[ 6.020000] <== exit_mmap()
As you can see, I have one warning that shows up "free page d07faee0:
refcount not one: 0".
When reverting your patch, I don't have this warning:
[ 6.320000] ==> do_mmap_pgoff(,0,36000,7,2,0)
[ 6.320000] xxxalloc order 6 for 36000yyy
[ 6.320000] xxxshave 8/10 @64yyy
[ 6.320000] xxxshave 2/2 @56yyy
[ 6.320000] ==> add_vma_to_mm(,d0781600)
[ 6.320000] <== do_mmap_pgoff() = d0540000
[ 6.340000] ==> do_mmap_pgoff(,0,2000,3,4000021,0)
[ 6.340000] xxxalloc order 1 for 2000yyy
[ 6.340000] ==> add_vma_to_mm(,d0781720)
[ 6.340000] <== do_mmap_pgoff() = d0536000
[ 6.350000] ==> exit_mmap()
[ 6.350000] ==> delete_vma_from_mm(d0781720)
[ 6.350000] ==> delete_vma(d0781720)
[ 6.350000] ==> __put_nommu_region(d078f0f0{1})
[ 6.350000] xxxfree seriesyyy
[ 6.350000] xxx- free d0536000yyy
[ 6.350000] xxx- free d0537000yyy
[ 6.350000] ==> delete_vma_from_mm(d0781600)
[ 6.350000] ==> delete_vma(d0781600)
[ 6.350000] ==> __put_nommu_region(d078f120{1})
[ 6.350000] xxxfree seriesyyy
[ 6.350000] xxx- free d0540000yyy
[ 6.350000] xxx- free d0541000yyy
[ 6.350000] xxx- free d0542000yyy
</snip>
[ 6.370000] xxx- free d0572000yyy
[ 6.370000] xxx- free d0573000yyy
[ 6.370000] xxx- free d0574000yyy
[ 6.370000] xxx- free d0575000yyy
[ 6.370000] <== exit_mmap()
Do you have an idea on what could cause the issue?
I can do any tests you could find relevant to hunt down this bug.
Best regards,
Maxime
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