linux-kernel - Re: [PATCH] dax/kmem: Pass valid argument to memory_group_register

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Message-ID: <b7e620efa0de6b9f7a8ae9ce51d8dd562f384cdc.camel@intel.com>
Date:   Wed, 21 Jun 2023 06:42:45 +0000
From:   "Verma, Vishal L" <vishal.l.verma@...el.com>
To:     "Schofield, Alison" <alison.schofield@...el.com>,
        "tsahu@...ux.ibm.com" <tsahu@...ux.ibm.com>
CC:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aneesh.kumar@...ux.ibm.com" <aneesh.kumar@...ux.ibm.com>,
        "jaypatel@...ux.ibm.com" <jaypatel@...ux.ibm.com>
Subject: Re: [PATCH] dax/kmem: Pass valid argument to
 memory_group_register_static

On Wed, 2023-06-21 at 11:36 +0530, Tarun Sahu wrote:
> Hi Alison,
> 
> Alison Schofield <alison.schofield@...el.com> writes:
> 
> > On Tue, Jun 20, 2023 at 07:33:32PM +0530, Tarun Sahu wrote:
> > > memory_group_register_static takes maximum number of pages as the argument
> > > while dev_dax_kmem_probe passes total_len (in bytes) as the argument.
> > 
> > This sounds like a fix. An explanation of the impact and a fixes tag
> > may be needed. Also, wondering how you found it.
> > 
> Yes, it is a fix, I found it during dry code walk-through.
> There is not any impact as such. As,
> memory_group_register_static just set the max_pages limit which
> is used in auto_movable_zone_for_pfn to determine the zone.
> 
> which might cause these condition to behave differently,
> 
> This will be true always so jump will happen to kernel_zone
>         if (!auto_movable_can_online_movable(NUMA_NO_NODE, group, nr_pages))
>                 goto kernel_zone;
> ---
> kernel_zone:
>         return default_kernel_zone_for_pfn(nid, pfn, nr_pages);
> 
> ---
> 
> Here, In below, zone_intersects compare range will be larger as nr_pages
> will be higher (derived from total_len passed in dev_dax_kmem_probe).
> 
> static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn,
>                 unsigned long nr_pages)
> {
>         struct pglist_data *pgdat = NODE_DATA(nid);
>         int zid;
> 
>         for (zid = 0; zid < ZONE_NORMAL; zid++) {
>                 struct zone *zone = &pgdat->node_zones[zid];
> 
>                 if (zone_intersects(zone, start_pfn, nr_pages))
>                         return zone;
>         }
> 
>         return &pgdat->node_zones[ZONE_NORMAL];
> }
> 
> In Mostly cases, ZONE_NORMAL will be returned. But there is no
> crash/panic issues involved here, only decision making on selecting zone
> is affected.
> 

Hi Tarun,

Good find! With a Fixes tag, and perhaps inclusion of a bit more of
this detail described in the commit message, feel free to add:

Reviewed-by: Vishal Verma <vishal.l.verma@...el.com>