linux-kernel - Re: [PATCH v2 2/2] dax: add a sysfs knob to control memmap_on

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Message-ID: <ee14082752fd634d7b619b7dd438170fdc0bbe1a.camel@intel.com>
Date:   Fri, 8 Dec 2023 21:24:24 +0000
From:   "Verma, Vishal L" <vishal.l.verma@...el.com>
To:     "lizhijian@...itsu.com" <lizhijian@...itsu.com>,
        "Jiang, Dave" <dave.jiang@...el.com>
CC:     "david@...hat.com" <david@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>
Subject: Re: [PATCH v2 2/2] dax: add a sysfs knob to control memmap_on_memory
 behavior

On Fri, 2023-12-08 at 09:20 +0000, Zhijian Li (Fujitsu) wrote:
> 
> 
> On 08/12/2023 03:25, Verma, Vishal L wrote:
> > On Thu, 2023-12-07 at 08:29 +0000, Zhijian Li (Fujitsu) wrote:
> > > Hi Vishal,
> > > 
> > > 
> > > On 07/12/2023 12:36, Vishal Verma wrote:
> > > > +
> > > > +What:          /sys/bus/dax/devices/daxX.Y/memmap_on_memory
> > > > +Date:          October, 2023
> > > > +KernelVersion: v6.8
> > > > +Contact:       nvdimm@...ts.linux.dev
> > > > +Description:
> > > > +               (RW) Control the memmap_on_memory setting if the dax device
> > > > +               were to be hotplugged as system memory. This determines whether
> > > > +               the 'altmap' for the hotplugged memory will be placed on the
> > > > +               device being hotplugged (memmap_on+memory=1) or if it will be
> > > 
> > > s/memmap_on+memory=1/memmap_on_memory=1
> > 
> > Thanks, will fix.
> > > 
> > > 
> > > I have a question here
> > > 
> > > What relationship about memmap_on_memory and 'ndctl-create-namespace
> > > -M' option which
> > > specifies where is the vmemmap backed memory.
> > > I'm confused that memmap_on_memory=1 and '-M dev' are the same for
> > > nvdimm devdax mode ?
> > > 
> > The main difference is that memory that comes from non-nvdimm sources,
> > such as hmem, or cxl, doesn't have a chance to set up the altmaps as
> > pmem can with '-M dev'. For these, memmap_on_memory does this as part
> > of the memory hotplug.
> 
> Thanks for your explanation.
> (I wrongly thought nvdimm.kmem was also controlled by '-M dev' before)
> 
> feel free add:
> Tested-by: Li Zhijian <lizhijian@...itsu.com>

Thank you Zhijian!