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Subject: Re: [PATCH] mm, numa: fix bad pmd by atomically check for
 pmd_trans_huge when marking page tables prot_numa
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <20200309150531.GD25642@optiplex-lnx>
Date:   Tue, 10 Mar 2020 20:04:11 -0400
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        mgorman <mgorman@techsingularity.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>
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References: <20200216191800.22423-1-aquini@redhat.com>
 <2E0766B8-DDD1-4448-8605-8535A16670FC@lca.pw> <20200307030530.GB4093@t490s>
 <9124C8B9-FB47-44F5-8606-DD9261BCB383@lca.pw> <20200308231423.GA22348@t490s>
 <C5CED45A-FFDA-46C7-A116-284431CF5940@lca.pw>
 <20200309150531.GD25642@optiplex-lnx>
To:     Rafael Aquini <aquini@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Mar 9, 2020, at 11:05 AM, Rafael Aquini <aquini@redhat.com> wrote:
> I'm still waiting on a similar system to become available, so I can
> work on your reproducer case, as well as to dig and wrap my head =
around it.
>=20
> I still don't think that skipping the pmd_none() in the =
change-protection walk=20
> should cause a big fuss like you observed here (yet, it seems it =
does), and=20
> the fact that we need that race window to take the __split_huge_pmd() =
suggests,
> at least to me, that we might be missing this proper split somewhere =
else.

I have sent out another patch which should be more correct,

https://lore.kernel.org/lkml/20200310235846.1319-1-cai@lca.pw/=