Excessive xfs_inode allocations trigger OOM killer

From: Florian Weimer <fw@deneb.enyo.de>
To: xfs@oss.sgi.com
Subject: Excessive xfs_inode allocations trigger OOM killer
Date: Tue, 20 Sep 2016 21:48:42 +0200	[thread overview]
Message-ID: <87a8f2pd2d.fsf@mid.deneb.enyo.de> (raw)

I have an amd64 4.7.1 system (upstream kernel, pretty regular config)
with a small file system:

Filesystem     1K-blocks      Used Available Use% Mounted on
/dev/sda1      922595184 800396464 122198720  87% /
Filesystem        Inodes    IUsed     IFree IUse% Mounted on
/dev/sda1      504110496 15305094 488805402    4% /

The odd thing is that after a while, XFS consumes a lot of memory
according to slabtop:

  OBJS ACTIVE  USE OBJ SIZE  SLABS OBJ/SLAB CACHE SIZE NAME                   
4121208 4121177  99%    0.88K 1030302        4   4121208K xfs_inode
986286 985229  99%    0.19K  46966       21    187864K dentry
723255 723076  99%    0.10K  18545       39     74180K buffer_head
270263 269251  99%    0.56K  38609        7    154436K radix_tree_node
140310  67409  48%    0.38K  14031       10     56124K mnt_cache

(I have attached the /proc/meminfo contents in case it offers further
clues.)

Confronted with large memory allocations (from “make -j12” and
compiling GCC, so perhaps ~8 GiB of memory), the OOM killer kicks in
and kills some random process.  I would have expected that some
xfs_inodes are freed instead.

I don't think this is an ordinary memory leak.  The last time I saw
something like the slabtop output above, I could do “sysctl
vm.drop_caches = 3”, and the amount of memory allocated reported by
slabtop was reduced considerably.  (I have not checked if the memory
was actually returned to the system.)  I have not done this now so
that I can gather further data for debugging.  I am not sure what
triggers this huge allocation.  It could be related to my Gnus mail
spool (which contains lots and lots of small files).

MemTotal:       12300808 kB
MemFree:         1744132 kB
MemAvailable:   10325076 kB
Buffers:               0 kB
Cached:          4726892 kB
SwapCached:           32 kB
Active:          3094868 kB
Inactive:        2307968 kB
Active(anon):     303736 kB
Inactive(anon):   738188 kB
Active(file):    2791132 kB
Inactive(file):  1569780 kB
Unevictable:          32 kB
Mlocked:              32 kB
SwapTotal:      14645244 kB
SwapFree:       14644796 kB
Dirty:                28 kB
Writeback:             0 kB
AnonPages:        676016 kB
Mapped:           290956 kB
Shmem:            365980 kB
Slab:            4646696 kB
SReclaimable:    4542188 kB
SUnreclaim:       104508 kB
KernelStack:        8112 kB
PageTables:        18148 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    20795648 kB
Committed_AS:    4926352 kB
VmallocTotal:   34359738367 kB
VmallocUsed:           0 kB
VmallocChunk:          0 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:      609792 kB
DirectMap2M:    11964416 kB
DirectMap1G:     2097152 kB

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