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(cpe5c7695f3aee0-cm5c7695f3aede.cpe.net.cable.rogers.com. [99.254.144.39]) by smtp.gmail.com with ESMTPSA id px13-20020a056214050d00b0062607ea6d01sm1400792qvb.50.2023.06.02.16.05.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 02 Jun 2023 16:06:00 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: David Hildenbrand , Alistair Popple , Andrew Morton , Andrea Arcangeli , "Kirill A . Shutemov" , Johannes Weiner , John Hubbard , Naoya Horiguchi , peterx@redhat.com, Muhammad Usama Anjum , Hugh Dickins , Mike Rapoport Subject: [PATCH 2/4] mm/migrate: Unify and retry an unstable pmd when hit Date: Fri, 2 Jun 2023 19:05:50 -0400 Message-Id: <20230602230552.350731-3-peterx@redhat.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230602230552.350731-1-peterx@redhat.com> References: <20230602230552.350731-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" There's one pmd_bad() check, but should be better to use pmd_clear_bad() which is part of pmd_trans_unstable(). And I assume that's not enough, because there can be race of thp insertion when reaching pmd_bad(), so it can be !bad but a thp, then the walk is illegal. There's one case though where the function used pmd_trans_unstable() but only for pmd split. Merge them into one, and if it happens retry the whole pmd. Cc: Alistair Popple Cc: John Hubbard Signed-off-by: Peter Xu --- mm/migrate_device.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index d30c9de60b0d..6fc54c053c05 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -83,9 +83,6 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, if (is_huge_zero_page(page)) { spin_unlock(ptl); split_huge_pmd(vma, pmdp, addr); - if (pmd_trans_unstable(pmdp)) - return migrate_vma_collect_skip(start, end, - walk); } else { int ret; =20 @@ -106,8 +103,10 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, } } =20 - if (unlikely(pmd_bad(*pmdp))) - return migrate_vma_collect_skip(start, end, walk); + if (unlikely(pmd_trans_unstable(pmdp))) { + walk->action =3D ACTION_AGAIN; + return 0; + } =20 ptep =3D pte_offset_map_lock(mm, pmdp, addr, &ptl); arch_enter_lazy_mmu_mode(); --=20 2.40.1