Re: [PATCH] VM: kswapd should not do blocking memory allocations

Wu Fengguang
2010-08-20T05:40:21Z

On Wed, Aug 18, 2010 at 03:04:01PM -0400, Trond Myklebust wrote:
> From: Trond Myklebust <Trond.Myklebust@netapp.com>
>
> Allowing kswapd to do GFP_KERNEL memory allocations (or any blocking memory
> allocations) is wrong and can cause deadlocks in try_to_release_page(), as
> the filesystem believes it is safe to allocate new memory and block,
> whereas kswapd is there specifically to clear a low-memory situation...
>
> Set the gfp_mask to GFP_IOFS instead.

It would be more descriptive to say "remove the __GFP_WAIT bit".

The change looks reasonable _in itself_, since we always prefer to
avoid unnecessary waits for kswapd. So

Acked-by: Wu Fengguang <fengguang.wu@intel.com>

> Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
> ---
>
> mm/vmscan.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ec5ddcc..716dd16 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2095,7 +2095,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
> unsigned long total_scanned;
> struct reclaim_state *reclaim_state = current->reclaim_state;
> struct scan_control sc = {
> - .gfp_mask = GFP_KERNEL,
> + .gfp_mask = GFP_IOFS,
> .may_unmap = 1,
> .may_swap = 1,
> /*
>
> --
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