We've started experimenting with larger directory block sizes to avoid
directory fragmentation. Everything seems to work fine, except that the log
is spammed with these lovely debug messages:
XFS: possible memory allocation deadlock in kmem_alloc (mode:0x250)
>From looking at the code, it looks like that each of those messages (there
are thousands) equates to 100 trips through the loop. My guess is that the
larger blocks require multi-page allocations which are harder to satisfy.
This is with 3.10 kernel.
The hardware is something like (I can find out the exact config is you want):
128 GB RAM
LSI 9271-8i RAID (one big RAID-60 with 36 disks, partitioned)
As I hinted at earlier, we end up with pretty big directories. We can
semi-reliably trigger this when we run rsync on the data between two
(identical) hosts over 10GbitE.
# xfs_info /dev/sda9
meta-data=/dev/sda9 isize=256 agcount=6, agsize=268435455 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=1454213211, imaxpct=5
= sunit=0 swidth=0 blks
naming =version 2 bsize=65536 ascii-ci=0
log =internal bsize=4096 blocks=521728, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
sysrq m output: https://www.copy.com/s/mYfMYfJJl2EB/sysrq-m.txt
While I realize that the message isn't bad, it does mean that the system is
having hard time allocating memory. This could potentially lead to bad
performance, or even an actual deadlock. Do you have any suggestions?
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.
- George Bernard Shaw