On Mon, 2005-02-14 at 18:57, Andrew Morton wrote: > Badari Pulavarty <[EMAIL PROTECTED]> wrote: > > > > Most of DB2 customers use filesystem for their database. Under the load, > > they complain that entire memory in the system is used by filesystem > > pagecache, freememory is very low and system starts swapping crazy OR > > see lots of memory allocation failures and OOM killer kills db2. > > slabinfo shows lots of bufferheads and VM folks claim that, bufferheads > > are holding a ref. on the pages, so they can't use them. So, I want > > to find the truth in the story and findout what exactly happening here > > and which one to blame (VM or FS or IO problems) ? > > > > BTW, all these on 2.4 kernels and I don't have a reproducible testcase > > :( > > > > Feb 7 05:35:17 nmcopsu41 kernel: ENOMEM in do_get_write_access, > > retrying. > > Do these machines have a large amount of highmem? > > If so, yes, you can oom because lots of highmem pages have buffer_heads > attached and you've run out of lowmem. The 2.4 VM will go off looking for > lowmem pages to reclaim and will ignore the highmem pages because there's > no highmem shortage. Consequently those buffer_heads don't get freed up > and we're unable to reclaim any lowmem -> oom. > > Andrea did a patch along time ago (it'll be in suse 2.4 kernels) which, > under these circumstances, strip the buffers from those highmem pages when > they're encountered on the LRU. From a quick read it seems that that patch > is not in current 2.4 kernels. > > It's harder to do that in 2.6 because we have a separate LR per zone.
Our DB2 folks *claims* to have seen this problem both on ia32 and AMD64 customers. So, I am not sure if its really only highmem related. Only workaround seems to be configure DB2 to not to use more than 1.5GB on a 8GB RAM system :( I have nothing much to go on, other than looking data from a sick machine. What should I be looking at, to narrow down the problem some more ? BTW, none of these BIG customers will take a patch to figure out whats happening (since its on their production system) :( Thanks, Badari - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
