linux-kernel - Re: [PATCH v3 00/15] HWPOISON: soft offline rework

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Date:   Tue, 30 Jun 2020 06:50:59 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Oscar Salvador <osalvador@...e.de>
CC:     "nao.horiguchi@...il.com" <nao.horiguchi@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "aneesh.kumar@...ux.vnet.ibm.com" <aneesh.kumar@...ux.vnet.ibm.com>,
        "zeil@...dex-team.ru" <zeil@...dex-team.ru>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 00/15] HWPOISON: soft offline rework

On Mon, Jun 29, 2020 at 12:29:25PM +0200, Oscar Salvador wrote:
> On Wed, 2020-06-24 at 15:01 +0000, nao.horiguchi@...il.com wrote:
> > I rebased soft-offline rework patchset [1][2] onto the latest
> > mmotm.  The
> > rebasing required some non-trivial changes to adjust, but mainly that
> > was
> > straightforward.  I confirmed that the reported problem doesn't
> > reproduce on
> > compaction after soft offline.  For more precise description of the
> > problem
> > and the motivation of this patchset, please see [2].
> 
> Hi Naoya,
> 
> Thanks for dusting this off.
> To be honest, I got stuck with the hard offline mode so this delayed
> the resubmission, along other problems.
> 
> > I think that the following two patches in v2 are better to be done
> > with
> > separate work of hard-offline rework, so it's not included in this
> > series.
> > 
> >   - mm,hwpoison: Take pages off the buddy when hard-offlining
> >   - mm/hwpoison-inject: Rip off duplicated checks
> > 
> > These two are not directly related to the reported problem, so they
> > seems
> > not urgent.  And the first one breaks num_poisoned_pages counting in
> > some
> > testcases, and The second patch needs more consideration about
> > commented point.
> 
> I fully agree.
> 
> > Any comment/suggestion/help would be appreciated.
> 
> My "new" version included a patch to make sure we give a chance to
> pages that possibly are in a pcplist.
> Current behavior is that if someone tries to soft-offline such a page,
> we return an error because page count is 0 but page is not in the buddy
> system.
> 
> Since this patchset already landed in the mm tree, I could send it as a
> standalone patch on top if you agree with it.
> 
> My patch looked something like:
> 
> From: Oscar Salvador <osalvador@...e.de>
> Date: Mon, 29 Jun 2020 12:25:11 +0200
> Subject: [PATCH] mm,hwpoison: Drain pcplists before bailing out for
> non-buddy
>  zero-refcount page
> 
> A page with 0-refcount and !PageBuddy could perfectly be a pcppage.
> Currently, we bail out with an error if we encounter such a page,
> meaning that we do not give a chance to handle pcppages.
> 
> Fix this by draining pcplists whenever we find this kind of page
> and retry the check again.
> It might be that pcplists have been spilled into the buddy allocator
> and so we can handle it.
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>

I'm fine with this patch, so this will be with the next version with
some minor change like moving function comment block together.

Actually I feel we could refactor get_hwpoison_page() with get_any_page()
to handle this kind of pcplist related issues in one place. But this could
be more important in hard-offline reworking, and we don't have to do it
in this series.

Thanks,
Naoya Horiguchi