Re: [PATCH 3/3] mm: when handling percpu_pagelist_fraction, useon_each_cpu() to set percpu pageset fields.

[Gilad Ben-Yossef]

On Fri, Apr 5, 2013 at 11:33 PM, Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx> wrote:
> In free_hot_cold_page(), we rely on pcp->batch remaining stable.
> Updating it without being on the cpu owning the percpu pageset
> potentially destroys this stability.
>
> Change for_each_cpu() to on_each_cpu() to fix.

Are you referring to this? -

1329         if (pcp->count >= pcp->high) {
1330                 free_pcppages_bulk(zone, pcp->batch, pcp);
1331                 pcp->count -= pcp->batch;
1332         }

I'm probably missing the obvious but won't it be simpler to do this in
 free_hot_cold_page() -

1329         if (pcp->count >= pcp->high) {
1330                  unsigned int batch = ACCESS_ONCE(pcp->batch);
1331                 free_pcppages_bulk(zone, batch, pcp);
1332                 pcp->count -= batch;
1333         }

Now the batch value used is stable and you don't have to IPI every CPU
in the system just to change a config knob...

Thanks,
Gilad



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Gilad Ben-Yossef
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