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

From: Gilad Ben-Yossef
Date: Mon Apr 08 2013 - 08:20:51 EST

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...


Gilad Ben-Yossef
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