[Lustre-discuss] lustre ram usage (contd)
Balagopal Pillai
pillai at mathstat.dal.ca
Mon Dec 24 08:09:26 PST 2007
Hi Andreas,
Thanks. The two OSS also export two ext3 volumes each via NFS
that are used
to backup the 4 smaller Lustre volumes. One possibility as you
mentioned, is that the memory consumption is not Lustre related, but
ext3 related, as the destination ext3 volumes are also coming from the
same OSS servers, but mounted over NFS on the Lustre client that does
the rsync.
I upgraded the ram today morning on both OSS from 4 G to 8 G
and hope the ram on both OSS is enough for both Lustre operations and
the rsync backup.
Regards
Balagopal
Andreas Dilger wrote:
> On Dec 23, 2007 18:01 -0400, Balagopal Pillai wrote:
>
>> The cluster is made idle on the weekend to look at the Lustre
>> ram consumpton issue. The ram used during yesterday's rsync is still not
>> freed up. Here is the output from free
>>
>> total used free shared buffers cached
>> Mem: 4041880 3958744 83136 0 876132 144276
>> -/+ buffers/cache: 2938336 1103544
>> Swap: 4096564 240 4096324
>>
>
> Note that this is normal behaviour for Linux. Ram that is unused provides
> no value, so all available RAM is used for cache until something else is
> needing to use this memory.
>
>
>> Looking at vmstat -m, there is something odd. Seems like
>> ext3_inode_cache and dentry_cache seems to be the biggest occupants of
>> ram. ldiskfs_inode_cache comparatively smaller.
>> -
>>
>> Cache Num Total Size Pages
>> ldiskfs_inode_cache 430199 440044 920 4
>> ldlm_locks 10509 12005 512 7
>> ldlm_resources 10291 11325 256 15
>> buffer_head 230970 393300 88 45
>>
>
>
>> ext3_inode_cache 1636505 1636556 856 4
>> dentry_cache 1349923 1361216 240 16
>>
>
> This is odd, because Lustre doesn't use ext3 at all. It uses ldiskfs
> (which is ext3 renamed + patches), so it is some non-Lustre filesystem
> usage which is consuming most of your memory.
>
>
>> Is there anything in proc as explained in
>> http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/ref-guide/s1-proc-directories.html
>> that can force the kernel to flush out the dentry_cache and
>> ext3_inode_cache when the rsync is over and cache is not needed anymore?
>> Thanks very much.
>>
>
> Only to unmount and remount the filesystem, on the server. On Lustre
> clients there is a mechanism to flush Lustre cache, but that doesn't
> help you here.
>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.
>
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