Re: [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR_DEPLETED on UP

[Leon Romanovsky]

Hi Mel,
>         __mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
> -       if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 &&
> +       if (zone_page_state(zone, NR_ALLOC_BATCH) <= 0 &&
zone_page_state is declared to return unsigned long value [1], so it
should never be below 0.
So interesting question: what zone_page_state will return for negative
atomic_long_read(&zone->vm_stat[item]) ?

130 static inline unsigned long zone_page_state(struct zone *zone,
131                                         enum zone_stat_item item)
132 {
133         long x = atomic_long_read(&zone->vm_stat[item]);
134 #ifdef CONFIG_SMP
135         if (x < 0)
136                 x = 0;
137 #endif
138         return x;
139 }

[1] https://git.kernel.org/cgit/linux/kernel/git/mhocko/mm.git/tree/include/linux/vmstat.h#n130

-- 
Leon Romanovsky | Independent Linux Consultant
        www.leon.nu | leon@xxxxxxx
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