linux-kernel - Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on

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Date:   Wed, 2 Aug 2023 06:02:12 +0000
From:   "Verma, Vishal L" <vishal.l.verma@...el.com>
To:     "Huang, Ying" <ying.huang@...el.com>,
        "aneesh.kumar@...ux.ibm.com" <aneesh.kumar@...ux.ibm.com>
CC:     "david@...hat.com" <david@...hat.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "jmoyer@...hat.com" <jmoyer@...hat.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on_memory requests
 across memblocks

On Mon, 2023-07-24 at 11:16 +0800, Huang, Ying wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com> writes:
> > 
> > > @@ -1339,27 +1367,20 @@ int __ref add_memory_resource(int nid,
> > > struct resource *res, mhp_t mhp_flags)
> > >         /*
> > >          * Self hosted memmap array
> > >          */
> > > -       if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
> > > -               if (!mhp_supports_memmap_on_memory(size)) {
> > > -                       ret = -EINVAL;
> > > +       if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
> > > +           mhp_supports_memmap_on_memory(memblock_size)) {
> > > +               for (cur_start = start; cur_start < start + size;
> > > +                    cur_start += memblock_size) {
> > > +                       ret = add_memory_create_devices(nid,
> > > group, cur_start,
> > > +                                                       memblock_
> > > size,
> > > +                                                       mhp_flags
> > > );
> > > +                       if (ret)
> > > +                               goto error;
> > > +               }
> > 
> > We should handle the below error details here. 
> > 
> > 1) If we hit an error after some blocks got added, should we
> > iterate over rest of the dev_dax->nr_range.
> > 2) With some blocks added if we return a failure here, we remove
> > the
> > resource in dax_kmem. Is that ok? 
> > 
> > IMHO error handling with partial creation of memory blocks in a
> > resource range should be
> > documented with this change.
> 
> Or, should we remove all added memory blocks upon error?
> 
I didn't address these in v3 - I wasn't sure how we'd proceed here.
Something obviously went very wrong and I'd imagine it is okay if this
memory is unusable as a result.

What woyuld removing the blocks we added look like? Just call
try_remove_memory() from the error path in add_memory_resource()? (for
a range of [start, cur_start) ?