linux-kernel - Re: [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR

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Message-ID: <CALq1K=JO2b-=iq40RRvK8JFFbrzyH5EyAp5jyS50CeV0P3eQcA@mail.gmail.com>
Date:	Sun, 7 Sep 2014 09:32:20 +0300
From:	Leon Romanovsky <leon@...n.nu>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] mm: page_alloc: Fix setting of ZONE_FAIR_DEPLETED on UP

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@...n.nu
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