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
>>> @@ -1435,8 +1435,10 @@ loop_again:
>>> unsigned long lru_pages = 0;
>>>
>>> /* The swap token gets in the way of swapout... */
>>> - if (!priority)
>>> + if (!priority) {
>>> + synchronize_rcu();
>
> Bah, it seems I send the wrong patch out :-/
>
Looks like I reviewed the wrong thing then :-)
> this is the one against disable_swap_token(). I meant to send out this
> one:
>
> @@ -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);
> + }
>
>
>> Interesting change
>>
>> 1. I suspect that synchronize_rcu() is most likely to free up
>> slab pages, so shrink_slab() will clean up all the freed
>> pages. Could we add a comment to indicate the same?
>
> Yes indeed, will add such a comment.
>
>> 2. Shouldn't we do this in balance_pgdat() as well?
>
> Uhm, this is balance_pgdat() (both these changes) :-)
>
Hmm.. Could you please generate the diff with -p.
> 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?
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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