Red Hat Bugzilla – Bug 447667
Memory leak in kernel-18.104.22.168-18.fc9.x86_64
Last modified: 2009-07-14 11:47:42 EDT
Description of problem:
This morning I noticed that firefox had crashed overnight, and the desktop was
behaving very slow, as if the machine were swapping heavily. I expected to see
some bloated process in "top"s output, but after sorting the processes by
memory, I saw nothing unusual. Applications were fairly normal, but there was
very little free memory.
Next, I turned to /proc/meminfo, and it looks like the kernel had allocated
1.4GB of slab! According to the slabinfo file, there were nearly 7 million
dentry slabs "active" (if I'm reading it correctly). I don't really understand
the dentry cache, but it seems odd to have 7M dentry caches when I have fewer
than 500k files and directories total on all of the mounted filesystems.
There's nothing odd in the logs except this:
May 20 03:24:44 herald kernel: printk: 37 messages suppressed.
The kernel didn't print any messages in several hours prior to 3:24, and nothing
afterward until I rebooted the system. Unfortunately, I didn't check "dmesg"
before rebooting. :(
Not much was running overnight: I was logged in to Gnome, Thunderbird and
Firefox were running, and so was Miro.
Version-Release number of selected component (if applicable):
Created attachment 306202 [details]
copy of /proc/meminfo made before reboot
Created attachment 306203 [details]
copy of /proc/slabinfo made before reboot
if you can reproduce this, do this ..
$ echo 3 > /proc/sys/vm/drop_caches
that should purge the dentry cache (and other caches).
They should get reclaimed when something needs memory. This is the first report
I've seen so far of anything suggesting the kernel is leaking slab objects, and
something like a dentry leak would show up real quick.
Out of curiosity: what will purging the caches tell us about the problem?
I understand that cache items should be reclaimed when applications need memory.
I noticed that nearly all of the "Slab" allocated is marked "SReclaimable".
All the same, something caused Firefox to exit, and allocated a whole lot of
slab in a short amount of time. I'd wonder if Firefox was at fault, but I'm not
sure how it would cause the kernel to allocate a large amount of memory.
I haven't seen the problem manifest again, yet, but I'm not certain what caused
it in the first place.
I don't know if this is related, but I updated to a new kernel (Fed8) and this
kernel is unusable because of a memory leak. I have 3GB and it takes about 10-20
minutes to fill, then I need to reboot.
I went back a kernel using the boot/grub.conf option.
The kernel with a problem is 22.214.171.124-27.fc8
The kernel that runs ok is 126.96.36.199-10.fc8
I can provide additional information - let me know.
hm, I have some guess. (yup it's just _guess_)
1. dentry cache is "name to i-node number transration" cache.
Then many directory touched some command (e.g. find, updatedb) make bloat dentry cache easily.
some system run updatedb at midnight by cron. do you do that?
2. SLUB on NUMA dramatically increase dcache fragmentation at special situation. (its problem already fixed on upstream (IIRC 2.6.27)).
do you have a numa box?
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