Re: [PATCH] mm: thp: remove use_zero_page sysfs knob

From: Yang Shi
Date: Mon Jul 23 2018 - 17:52:55 EST




On 7/23/18 1:31 PM, David Rientjes wrote:
On Fri, 20 Jul 2018, Yang Shi wrote:

I agree to keep it for a while to let that security bug cool down, however, if
there is no user anymore, it sounds pointless to still keep a dead knob.

It's not a dead knob. We use it, and for reasons other than
CVE-2017-1000405. To mitigate the cost of constantly compacting memory to
allocate it after it has been freed due to memry pressure, we can either
continue to disable it, allow it to be persistently available, or use a
new value for use_zero_page to specify it should be persistently
available.

My understanding is the cost of memory compaction is *not* unique for huge zero page, right? It is expected when memory pressure is met, even though huge zero page is disabled.