On Mon, 24 Sep 2007 16:52:15 +0530 Balbir Singh
<[EMAIL PROTECTED]> wrote:
> Peter Zijlstra wrote:
> > On Mon, 24 Sep 2007 16:12:19 +0530 Balbir Singh
> > <[EMAIL PROTECTED]> wrote:
> >
> >> Peter Zijlstra wrote:
> >>> Just an idea I had, it seems like a good idea to wait for RCU callbacks
> >>> in reclaim so that we won't get all of memory stuck there.
> >>>
> >>> If this location is too aggressive we might stick it next to
> >>> disable_swap_token().
> >>>
> >>> ---
> >>> Couple RCU and reclaim.
> >>>
> >>> There could be a lot of memory stuck in RCU callbacks. Wait for RCU to
> >>> finish before giving it another go.
> >>>
> >>> Placed in kswapd and not direct reclaim path because kswapd never holds
> >>> rcu_read_lock() at this point and can thus not deadlock. Direct reclaim
> >>> callers might hold rcu_read_lock() and would suffer from deadlocks if
> >>> sync_rcu() were to be called.
> >>>
> >>> Signed-off-by: Peter Zijlstra <[EMAIL PROTECTED]>
> >>> ---
---
mm/vmscan.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -1527,8 +1527,10 @@ loop_again:
* OK, kswapd is getting into trouble. Take a nap, then take
* another pass across the zones.
*/
- if (total_scanned && priority < DEF_PRIORITY - 2)
+ if (total_scanned && priority < DEF_PRIORITY - 2) {
+ synchronize_rcu();
congestion_wait(WRITE, HZ/10);
+ }
/*
* We do this so kswapd doesn't build up large priorities for
> > Only kswapd can do this, direct reclaim has deadlock potential.
>
> Yes, but not in all cases, do you want to add any gfp_mask
> based smartness for direct reclaim?
gfp_mask doesn't carry the needed information. It depends on whether
the current context holds a rcu_read_lock().
so something like:
rcu_read_lock()
foo = kmalloc(sizeof(foo))
new_slab()
__alloc_pages()
try_to_free_pages()
synchronise_rcu() <-- deadlock
rcu_read_unlock()
-
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