On Tue, Apr 9, 2013 at 9:03 AM, Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx> wrote:
>
>> I also wonder whether there could be unexpected interactions between ->high
>> and ->batch not changing together atomically. For example, could adjusting
>> this knob cause ->batch to rise enough that it is greater than the previous
>> ->high? If the code above then runs with the previous ->high, ->count
>> wouldn't be correct (checking this inside free_pcppages_bulk() might help on
>> this one issue).
>
> You are right, but that can be treated in setup_pagelist_highmark() e.g.:
>
> 3993 static void setup_pagelist_highmark(struct per_cpu_pageset *p,
> 3994 unsigned long high)
> 3995 {
> 3996 struct per_cpu_pages *pcp;
> unsigned int batch;
> 3997
> 3998 pcp = &p->pcp;
> /* We're about to mess with PCP in an non atomic fashion.
> Put an intermediate safe value of batch and make sure it
> is visible before any other change */
> pcp->batch = 1UL;
> smb_mb();
>
> 3999 pcp->high = high;
and i think I missed another needed barrier here:
smp_mb();
>
> 4000 batch = max(1UL, high/4);
> 4001 if ((high/4) > (PAGE_SHIFT * 8))
> 4002 batch = PAGE_SHIFT * 8;
>
> pcp->batch = batch;
> 4003 }
>
--
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@xxxxxxxxxxxxx
Israel Cell: +972-52-8260388
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http://benyossef.com
"If you take a class in large-scale robotics, can you end up in a
situation where the homework eats your dog?"
-- Jean-Baptiste Queru
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