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();
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?
2. Shouldn't we do this in balance_pgdat() as well?
> disable_swap_token();
> + }
>
> all_zones_ok = 1;
>
> -
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--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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