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From:   Pavel Tatashin <pasha.tatashin@soleen.com>
Date:   Mon, 6 May 2019 14:18:20 -0400
Message-ID: <CA+CK2bAfjXCtRRV2DWy8huCvJ-y0L5cMvOh+9CS40WZfhx-aeg@mail.gmail.com>
Subject: Re: [v5 2/3] mm/hotplug: make remove_memory() interface useable
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        James Morris <jmorris@namei.org>,
        Sasha Levin <sashal@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Keith Busch <keith.busch@intel.com>,
        Vishal L Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Ross Zwisler <zwisler@kernel.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        Fengguang Wu <fengguang.wu@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Yaowei Bai <baiyaowei@cmss.chinamobile.com>,
        Takashi Iwai <tiwai@suse.de>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        David Hildenbrand <david@redhat.com>
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On Mon, May 6, 2019 at 2:04 PM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 5/6/19 11:01 AM, Dan Williams wrote:
> >>> +void __remove_memory(int nid, u64 start, u64 size)
> >>>  {
> >>> +
> >>> +     /*
> >>> +      * trigger BUG() is some memory is not offlined prior to calling this
> >>> +      * function
> >>> +      */
> >>> +     if (try_remove_memory(nid, start, size))
> >>> +             BUG();
> >>> +}
> >> Could we call this remove_offline_memory()?  That way, it makes _some_
> >> sense why we would BUG() if the memory isn't offline.
> > Please WARN() instead of BUG() because failing to remove memory should
> > not be system fatal.
>
> That is my preference as well.  But, the existing code BUG()s, so I'm
> OK-ish with this staying for the moment until we have a better handle on
> what all the callers do if this fails.

Yes, this is the reason why I BUG() here. The current code does this,
and I was not sure what would happen if we simply continue executing.
Of course, I would prefer to return failure, so the callers can act
appropriately, but let's make one thing at a time, this should not be
part of this series.

Thank you,
Pasha