Re: [PATCH RFC] mm: lru milestones, timestamps and ages

[Konstantin Khlebnikov <khlebnikov@openvz.org>]

Mel Gorman wrote:
> On Tue, Apr 30, 2013 at 03:02:14PM +0400, Konstantin Khlebnikov wrote:
>> +static inline bool
>> +is_lru_milestone(struct lruvec *lruvec, struct list_head *list)
>> +{
>> +	return unlikely(list>=&lruvec->milestones[0][0].lru&&
>> +			list<   &lruvec->milestones[NR_EVICTABLE_LRU_LISTS]
>> +						   [NR_LRU_MILESTONES].lru);
>> +}
>> +
>
> Not reviewing properly yet, just taking a quick look out of interest but
> this check may be delicate.  32-bit x86 machines start the kernel direct
> mapping at 0xC0000000 so milestones[0][0].lru will have some value betewen
> 0xC0000000 and 0xFFFFFFFF. HZ=250 on my distro config so after 0xC0000000
> jiffies or a bit over 149 days of uptime, it looks like there will be a
> window where LRU entries look like milestones. If I'm right, that is
> bound to cause problems.
>

Nope. There is no such dangerous magic. This function compares only pointers.
List heads in page LRU list can be either &page->lru or &lru_milestone->lru.
Since milestones are embedded into struct lruvec we can separate them in this way.

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