Re: memory leak in 2.6.11-rc2

[Nick Piggin]

Andrew Tridgell wrote:
> Andrew,
>
>  > So what you should do before generating the leak tool output is to put
>  > heavy memory pressure on the machine to try to get it to free up as much of
>  > that pagecache as possible.  bzero(malloc(lots)) will do it - create a real
>  > swapstorm, then do swapoff to kill remaining swapcache as well.
>
> As you saw when you logged into the machine earlier tonight, when you
> suspend the dbench processes and run a memory filler the memory is
> reclaimed.
>
> I still think its a bug though, as the oom killer is being triggered
> when it shouldn't be. I have 4G of ram in this machine, and I'm only
> running a couple of hundred processes that should be using maybe 500M
> in total, so for the oom killer to kick in might mean that the memory
> isn't being reclaimed under normal memory pressure. Certainly a ps
> shows no process using more than a few MB.
>
> The oom killer report is below. This is with 2.6.11-rc2, with the pipe
> leak fix, and the pgown monitoring patch. It was running one nbench of
> size 50 and one dbench of size 40 at the time.

There are various OOM killer improvements and fixes that have gone
into Andrew's kernel tree which should be included for 2.6.11.

I don't think the OOM killer was ever perfect in 2.6, but recent
tinkering in mm/ probably aggrivated it. *blush*

Here is another small OOM killer improvement. Previously we needed
to reclaim SWAP_CLUSTER_MAX pages in a single pass. That should be
changed so that we need only reclaim that many pages during the
entire try_to_free_pages run, without going OOM.

Andrea? Andrew? Look OK?


---

 linux-2.6-npiggin/mm/vmscan.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff -puN mm/vmscan.c~oom-helper mm/vmscan.c
--- linux-2.6/mm/vmscan.c~oom-helper	2005-01-25 23:04:28.000000000 +1100
+++ linux-2.6-npiggin/mm/vmscan.c	2005-01-25 23:05:06.000000000 +1100
@@ -914,12 +914,12 @@ int try_to_free_pages(struct zone **zone
 			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
 			reclaim_state->reclaimed_slab = 0;
 		}
-		if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) {
+		total_scanned += sc.nr_scanned;
+		total_reclaimed += sc.nr_reclaimed;
+		if (total_reclaimed >= SWAP_CLUSTER_MAX) {
 			ret = 1;
 			goto out;
 		}
-		total_scanned += sc.nr_scanned;
-		total_reclaimed += sc.nr_reclaimed;
 
 		/*
 		 * Try to write back as many pages as we just scanned.  This

_