Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default

From: Aneesh Kumar K.V
Date: Wed Mar 06 2019 - 07:46:04 EST

On 3/6/19 5:14 PM, Michal SuchÃnek wrote:
On Wed, 06 Mar 2019 14:47:33 +0530
"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> wrote:

Dan Williams <dan.j.williams@xxxxxxxxx> writes:

On Thu, Feb 28, 2019 at 1:40 AM Oliver <oohall@xxxxxxxxx> wrote:

On Thu, Feb 28, 2019 at 7:35 PM Aneesh Kumar K.V
<aneesh.kumar@xxxxxxxxxxxxx> wrote:
Also even if the user decided to not use THP, by
echo "never" > transparent_hugepage/enabled , we should continue to map
dax fault using huge page on platforms that can support huge pages.

Is this a good idea?

This knob is there for a reason. In some situations having huge pages
can severely impact performance of the system (due to host-guest
interaction or whatever) and the ability to really turn off all THP
would be important in those cases, right?

My understanding was that is not true for dax pages? These are not regular memory that got allocated. They are allocated out of /dev/dax/ or /dev/pmem*. Do we have a reason not to use hugepages for mapping pages in that case?