Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

[Andrew Lutomirski <luto@mit.edu>]

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I just booted 2.6.38.6 with exactly two patches applied.  Config was
the same as I emailed yesterday.  Userspace is F15.  First was
"aesni-intel: Merge with fpu.ko" because dracut fails to boot my
system without it.  Second was this (sorry for whitespace damage):

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0665520..3f44b81 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -307,7 +307,7 @@ static void set_reclaim_mode(int priority, struct
scan_control *sc,
         */
        if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
                sc->reclaim_mode |= syncmode;
-       else if (sc->order && priority < DEF_PRIORITY - 2)
+       else if ((sc->order && priority < DEF_PRIORITY - 2) ||
priority <= DEF_PRIORITY / 3)
                sc->reclaim_mode |= syncmode;
        else
                sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
@@ -1342,10 +1342,6 @@ static inline bool
should_reclaim_stall(unsigned long nr_taken,
        if (current_is_kswapd())
                return false;

-       /* Only stall on lumpy reclaim */
-       if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
-               return false;
-
        /* If we have relaimed everything on the isolated list, no stall */
        if (nr_freed == nr_taken)
                return false;

I started GNOME and Firefox, enabled swap, and ran test_mempressure.sh
1500 1400 1.  The system quickly gave the attached oops.

The oops was the ud2 here:

   0xffffffff810d251b <+215>:	mov    -0x28(%rbx),%rax
   0xffffffff810d251f <+219>:	test   $0x40,%al
   0xffffffff810d2521 <+221>:	je     0xffffffff810d2525 <shrink_page_list+225>
   0xffffffff810d2523 <+223>:	ud2

Please let me know what the next test to run is.

--Andy

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