On Sat, 8 Oct 2011, Shaohua Li wrote:
> has_under_min_watermark_zone is used to detect if there is GFP_ATOMIC allocation
> failure risk. For a high end_zone, if any zone below or equal to it has min
> matermark ok, we have no risk. But current logic is any zone has min watermark
> not ok, then we have risk. This is wrong to me.
>
> Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
> ---
> mm/vmscan.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> Index: linux/mm/vmscan.c
> ===================================================================
> --- linux.orig/mm/vmscan.c 2011-09-27 15:09:29.000000000 +0800
> +++ linux/mm/vmscan.c 2011-09-27 15:14:45.000000000 +0800
> @@ -2463,7 +2463,7 @@ loop_again:
>
> for (priority = DEF_PRIORITY; priority >= 0; priority--) {
> unsigned long lru_pages = 0;
> - int has_under_min_watermark_zone = 0;
> + int has_under_min_watermark_zone = 1;
bool
>
> /* The swap token gets in the way of swapout... */
> if (!priority)
> @@ -2594,9 +2594,10 @@ loop_again:
> * means that we have a GFP_ATOMIC allocation
> * failure risk. Hurry up!
> */
> - if (!zone_watermark_ok_safe(zone, order,
> + if (has_under_min_watermark_zone &&
> + zone_watermark_ok_safe(zone, order,
> min_wmark_pages(zone), end_zone, 0))
> - has_under_min_watermark_zone = 1;
> + has_under_min_watermark_zone = 0;
> } else {
> /*
> * If a zone reaches its high watermark,
Ignore checking the min watermark for a moment and consider if all zones
are above the high watermark (a situation where kswapd does not need to
do aggressive reclaim), then has_under_min_watermark_zone doesn't get
cleared and never actually stalls on congestion_wait(). Notice this is
congestion_wait() and not wait_iff_congested(), so the clearing of
ZONE_CONGESTED doesn't prevent this.
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