Re: kswapd in tight loop 2.6.9-rc3-bk-recent

From: Andrew Morton (akpm_at_osdl.org)
Date: 10/08/04

  • Next message: David S. Miller: "Re: UDP recvmsg blocks after select(), 2.6 bug?" 
    Date:	Thu, 7 Oct 2004 16:40:44 -0700
To: Chris Wright <chrisw@osdl.org>

    Chris Wright <chrisw@osdl.org> wrote:
    >
    > Is this known? Just came back from lunch, so I've no clue what kicked it
    > off. Profile below. (2.6.9-rc3-bk from yesterday, pending updates don't
    > appear to touch vmscan or mm/ in general).
    >
    > CPU: AMD64 processors, speed 1994.35 MHz (estimated)
    > Counted CPU_CLK_UNHALTED events (Cycles outside of halt state) with a
    > unit mask
    > of 0x00 (No unit mask) count 100000
    > samples % symbol name
    > 2410135 53.4092 balance_pgdat
    > 1328186 29.4329 shrink_zone
    > 555121 12.3016 shrink_slab
    > 84942 1.8823 __read_page_state

    Oh fanfuckingtastic. Something in there is failing to reach its
    termination condition. The code has become a trainwreck, so heaven knows
    what it was.

    For starters, let's actually use that local variable for something.

    We haven't been incrementing local variable total_scanned since the
    scan_control stuff went in.

    Signed-off-by: Andrew Morton <akpm@osdl.org> 

    ---
 25-akpm/mm/vmscan.c |    1 +
 1 files changed, 1 insertion(+)
diff -puN mm/vmscan.c~vmscan-total_scanned-fix mm/vmscan.c
--- 25/mm/vmscan.c~vmscan-total_scanned-fix	Thu Oct  7 16:31:55 2004
+++ 25-akpm/mm/vmscan.c	Thu Oct  7 16:31:55 2004
@@ -1054,6 +1054,7 @@ scan:
 			shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
 			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
 			total_reclaimed += sc.nr_reclaimed;
+			total_scanned += sc.nr_scanned;
 			if (zone->all_unreclaimable)
 				continue;
 			if (zone->pages_scanned > zone->present_pages * 2)
_
This probably won't fix it.
It looks like the code will lock up if all zones are out of unreclaimable
memory, but you won't be hitting that.
I also wonder if it'll lock up if just the first zone has ->all_unreclaimable.
I think a good starting point here will be to revert the most recent
change.
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  • Next message: David S. Miller: "Re: UDP recvmsg blocks after select(), 2.6 bug?"