linux-kernel - Re: [v5 2/3] mm/hotplug: make remove

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Message-ID: <CA+CK2bAfjXCtRRV2DWy8huCvJ-y0L5cMvOh+9CS40WZfhx-aeg@mail.gmail.com>
Date:   Mon, 6 May 2019 14:18:20 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        James Morris <jmorris@...ei.org>,
        Sasha Levin <sashal@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Keith Busch <keith.busch@...el.com>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Takashi Iwai <tiwai@...e.de>,
        Jérôme Glisse <jglisse@...hat.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [v5 2/3] mm/hotplug: make remove_memory() interface useable

On Mon, May 6, 2019 at 2:04 PM Dave Hansen <dave.hansen@...el.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