[PATCH] makedumpfile: change the wrong code to calculate bufsize_cyclic for elf dump

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>On Mon, May 19, 2014 at 07:15:38PM +0800, bhe at redhat.com wrote:
>
>[..]
>> -------------------------------------------------
>> bhe# cat /etc/kdump.conf
>> path /var/crash
>> core_collector makedumpfile -E --message-level 1 -d 31
>>
>> ------------------------------------------
>> kdump: dump target is /dev/sda2
>> kdump: saving [    9.595153] EXT4-fs (sda2): re-mounted. Opts:
>> data=ordered
>> to /sysroot//var/crash/127.0.0.1-2014.05.19-18:50:18/
>> kdump: saving vmcore-dmesg.txt
>> kdump: saving vmcore-dmesg.txt complete
>> kdump: saving vmcore
>>
>> calculate_cyclic_buffer_size, get_free_memory_size: 68857856
>>
>>  Buffer size for the cyclic mode: 27543142
>
>Bao,
>
>So 68857856 is 65MB. So we have around 65MB free when makedumpfile
>started.
>
>27543142  is 26MB. So we reserved 26MB for bitmaps or we reserved
>52MB for bitmaps?

52MB is correct, so the larry's view below looks right.

>Looking at the backtrace, larry pointed out few things.
>
>- makedumpfile has already allocated around 52MB of anonymous memory. I
>  guess this primarily comes from bitmaps and looks like we are reserving
>  52MB in bitmaps and not 26MB. I think this could be consistent with
>  current 80% logic as 80% of 65MB is around 52MB.
>
>	[   15.427173] Killed process 286 (makedumpfile) total-vm:79940kB,
>			anon-rss:54132kB, file-rss:892kB
>
>- So we are left with 65-52 = 13MB of total memory for kernel as well
>  as makedumpfile.
>
>- We have around 1500 pages in page cache which are in writeback stage.
>  That means around 6MB of pages are dirty and being written back to
>  disk. That means makedumpfile might not require lot of memory but
>  kernel does require free memory in dirty/writeback pages when dump
>  file is being written.
>
>	[   15.167732]  unevictable:7137 dirty:2 writeback:1511 unstable:0
>
>- Larry mentioend that there are around 5000 pages (20MB of memory)
>  sitting in file pages in page cache which ideally should be reclaimable.
>  It is not clear why that memory is not being reclaimed fast enough.
>
>	[   15.167732]  active_file:2406 inactive_file:2533 isolated_file:0
>
>So to me bottom line is that once the write out starts, kernel needs
>memory for holding dirty and writeback pages in cache too. So we probably
>are being too aggresive in allocating 80% of free memory for bitmaps. May
>be we should drop it down to 50-60%  of free memory for bitmaps.

I don't disagree to changing the 80% limit but I prefer to remove such
a percentage threshold because it's dependent on the environment.
Actually, I think it makes this problem more complex.

Now, thanks to page_is_buddy(), the performance degradation caused by
multi-cycle processing looks very small according to the benchmark on
2TB memory:

  https://lkml.org/lkml/2013/3/26/914

This result means we don't need to make an effort to allocate the bitmap
buffer as large as possible. So how about just setting a small fixed value
like 5MB as a safety limit?
It may be safer, and it will be easier to estimate the total memory usage of
makedumpfile, so I think it's better way if the most users especially large
machine users accept it.


Thanks
Atsushi Kumagai

>> Copying data                       : [ 15.9 %] -[   14.955468]
>> makedumpfile invoked oom-killer: gfp_mask=0x10200da, order=0,
>> oom_score_adj=0
>> [   14.963876] makedumpfile cpuset=/ mems_allowed=0
>> [   14.968723] CPU: 0 PID: 286 Comm: makedumpfile Not tainted
>> 3.10.0-123.el7.x86_64 #1
>> [   14.976606] Hardware name: Hewlett-Packard HP Z420 Workstation/1589,
>> BIOS J61 v01.02 03/09/2012
>> [   14.985567]  ffff88002fedc440 00000000f650c592 ffff88002fcb57d0
>> ffffffff815e19ba
>> [   14.993291]  ffff88002fcb5860 ffffffff815dd02d ffffffff810b68f8
>> ffff8800359dc0c0
>> [   15.001013]  ffffffff00000206 ffffffff00000000 0000000000000000
>> ffffffff81102e03
>> [   15.008733] Call Trace:
>> [   15.011413]  [<ffffffff815e19ba>] dump_stack+0x19/0x1b
>> [   15.016778]  [<ffffffff815dd02d>] dump_header+0x8e/0x214
>> [   15.022321]  [<ffffffff810b68f8>] ? ktime_get_ts+0x48/0xe0
>> [   15.028036]  [<ffffffff81102e03>] ? proc_do_uts_string+0xe3/0x130
>> [   15.034383]  [<ffffffff8114520e>] oom_kill_process+0x24e/0x3b0
>> [   15.040446]  [<ffffffff8106af3e>] ? has_capability_noaudit+0x1e/0x30
>> [   15.047068]  [<ffffffff81145a36>] out_of_memory+0x4b6/0x4f0
>> [   15.052864]  [<ffffffff8114b579>] __alloc_pages_nodemask+0xa09/0xb10
>> [   15.059482]  [<ffffffff81188779>] alloc_pages_current+0xa9/0x170
>> [   15.065711]  [<ffffffff811419f7>] __page_cache_alloc+0x87/0xb0
>> [   15.071804]  [<ffffffff81142606>]
>> grab_cache_page_write_begin+0x76/0xd0
>> [   15.078646]  [<ffffffffa02aa133>] ext4_da_write_begin+0xa3/0x330
>> [ext4]
>> [   15.085495]  [<ffffffff8114162e>]
>> generic_file_buffered_write+0x11e/0x290
>> [   15.092504]  [<ffffffff81143785>]
>> __generic_file_aio_write+0x1d5/0x3e0
>> [   15.099294]  [<ffffffff81050f00>] ?
>> rbt_memtype_copy_nth_element+0xa0/0xa0
>> [   15.106385]  [<ffffffff811439ed>] generic_file_aio_write+0x5d/0xc0
>> [   15.112841]  [<ffffffffa02a0189>] ext4_file_write+0xa9/0x450 [ext4]
>> [   15.119321]  [<ffffffff8117997c>] ? free_vmap_area_noflush+0x7c/0x90
>> [   15.125884]  [<ffffffff811af36d>] do_sync_write+0x8d/0xd0
>> [   15.131492]  [<ffffffff811afb0d>] vfs_write+0xbd/0x1e0
>> [   15.136839]  [<ffffffff811b0558>] SyS_write+0x58/0xb0
>> [   15.142091]  [<ffffffff815f2119>] system_call_fastpath+0x16/0x1b
>> [   15.148293] Mem-Info:
>> [   15.150770] Node 0 DMA per-cpu:
>> [   15.154138] CPU    0: hi:    0, btch:   1 usd:   0
>> [   15.159133] Node 0 DMA32 per-cpu:
>> [   15.162741] CPU    0: hi:   42, btch:   7 usd:  12
>> [   15.167732] active_anon:14395 inactive_anon:1034 isolated_anon:0
>> [   15.167732]  active_file:2406 inactive_file:2533 isolated_file:0
>> [   15.167732]  unevictable:7137 dirty:2 writeback:1511 unstable:0
>> [   15.167732]  free:488 slab_reclaimable:2371 slab_unreclaimable:3533
>> [   15.167732]  mapped:1110 shmem:1065 pagetables:166 bounce:0
>> [   15.167732]  free_cma:0
>> [   15.203076] Node 0 DMA free:508kB min:4kB low:4kB high:4kB
>> active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB
>> unevictabs
>> [   15.242882] lowmem_reserve[]: 0 128 128 128
>> [   15.247447] Node 0 DMA32 free:1444kB min:1444kB low:1804kB
>> high:2164kB active_anon:57580kB inactive_anon:4136kB active_file:9624kB
>> inacts
>> [   15.292683] lowmem_reserve[]: 0 0 0 0
>> [   15.296761] Node 0 DMA: 1*4kB (U) 1*8kB (U) 1*16kB (U) 1*32kB (U)
>> 1*64kB (U) 1*128kB (U) 1*256kB (U) 0*512kB 0*1024kB 0*2048kB 0*4096kB B
>> [   15.310372] Node 0 DMA32: 78*4kB (UEM) 52*8kB (UEM) 17*16kB (UM)
>> 12*32kB (UM) 2*64kB (UM) 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*40B
>> [   15.324412] Node 0 hugepages_total=0 hugepages_free=0
>> hugepages_surp=0 hugepages_size=2048kB
>> [   15.333088] 13144 total pagecache pages
>> [   15.337161] 0 pages in swap cache
>> [   15.340708] Swap cache stats: add 0, delete 0, find 0/0
>> [   15.346165] Free swap  = 0kB
>> [   15.349280] Total swap = 0kB
>> [   15.353385] 90211 pages RAM
>> [   15.356420] 53902 pages reserved
>> [   15.359880] 6980 pages shared
>> [   15.363088] 29182 pages non-shared
>> [   15.366719] [ pid ]   uid  tgid total_vm      rss nr_ptes swapents
>> oom_score_adj name
>> [   15.374788] [   85]     0    85    13020      553      24        0
>> 0 systemd-journal
>> [   15.383818] [  134]     0   134     8860      547      22        0
>> -1000 systemd-udevd
>> [   15.392664] [  146]     0   146     5551      245      23        0
>> 0 plymouthd
>> [   15.401167] [  230]     0   230     3106      537      16        0
>> 0 dracut-pre-pivo
>> [   15.410181] [  286]     0   286    19985    13756      55        0
>> 0 makedumpfile
>> [   15.418942] Out of memory: Kill process 286 (makedumpfile) score 368
>> or sacrifice child
>> [   15.427173] Killed process 286 (makedumpfile) total-vm:79940kB,
>> anon-rss:54132kB, file-rss:892kB
>> //lib/dracut/hooks/pre-pivot/9999-kdump.sh: line
>> Generating "/run/initramfs/rdsosreport.txt"
>>
>> >
>> >
>> > Thanks
>> > Atsushi Kumagai
>> >



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