linux-kernel - RE: XFS memory allocation deadlock in 2.6.38

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Date:	Mon, 28 Mar 2011 22:49:33 -0400
From:	Sean Noonan <Sean.Noonan@...sigma.com>
To:	'Dave Chinner' <david@...morbit.com>
CC:	'Michel Lespinasse' <walken@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Martin Bligh <Martin.Bligh@...sigma.com>,
	Trammell Hudson <Trammell.Hudson@...sigma.com>,
	Christos Zoulas <Christos.Zoulas@...sigma.com>,
	"linux-xfs@....sgi.com" <linux-xfs@....sgi.com>,
	Stephen Degler <Stephen.Degler@...sigma.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: XFS memory allocation deadlock in 2.6.38

> As it is, the question I'd really like answered is how a machine with
> 48GB RAM can possibly be short of memory when running mmap() on a
> 16GB file.  The error that XFS is throwing indicates that the
> machine cannot allocate a single page of memory, so where has all
> your memory gone, and why hasn't the OOM killer been let off the
> leash?  What is consuming the other 32GB of RAM or preventing it
> from being allocated? 
Here's meminfo while a test was deadlocking.  As you can see, we certainly aren't running out of RAM.
# cat /proc/meminfo 
MemTotal:       49551548 kB
MemFree:        44139876 kB
Buffers:            5324 kB
Cached:          4970552 kB
SwapCached:            0 kB
Active:            52772 kB
Inactive:        4960624 kB
Active(anon):      37864 kB
Inactive(anon):        0 kB
Active(file):      14908 kB
Inactive(file):  4960624 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:             0 kB
SwapFree:              0 kB
Dirty:           4914084 kB
Writeback:             0 kB
AnonPages:         37636 kB
Mapped:          4925460 kB
Shmem:               280 kB
Slab:             223212 kB
SReclaimable:     176280 kB
SUnreclaim:        46932 kB
KernelStack:        3968 kB
PageTables:        35228 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    47073968 kB
Committed_AS:      86556 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      380892 kB
VmallocChunk:   34331773836 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:        2048 kB
DirectMap2M:     2086912 kB
DirectMap1G:    48234496 kB


> Perhaps the output of xfs_bmap -vvp <file> after a successful vs
deadlocked run would be instructive....

I will try to get this tomorrow.

Sean
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