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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id p26sm2103753ood.28.2020.05.21.18.21.57 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Thu, 21 May 2020 18:21:57 -0700 (PDT) Date: Thu, 21 May 2020 18:21:42 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Anshuman Khandual cc: Hugh Dickins , Andrew Morton , Naoya Horiguchi , Zi Yan , John Hubbard , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH mmotm] mm/vmstat: Add events for PMD based THP migration without split fix In-Reply-To: Message-ID: References: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 22 May 2020, Anshuman Khandual wrote: > On 05/21/2020 07:19 PM, Hugh Dickins wrote: > > Fix 5.7-rc6-mm1 page migration crash in unmap_and_move(): when the > > page to be migrated has been freed from under us, that is considered > > a MIGRATEPAGE_SUCCESS, but no newpage has been allocated (and I don't > > think it would ever need to be counted as a successful THP migration). > > > > Signed-off-by: Hugh Dickins > > --- > > Fix to mm-vmstat-add-events-for-pmd-based-thp-migration-without-split.patch > > > > mm/migrate.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > --- 5.7-rc6-mm1/mm/migrate.c 2020-05-20 12:21:56.117693827 -0700 > > +++ linux/mm/migrate.c 2020-05-20 15:08:12.319476978 -0700 > > @@ -1248,7 +1248,7 @@ out: > > * we want to retry. > > */ > > if (rc == MIGRATEPAGE_SUCCESS) { > > - if (PageTransHuge(newpage)) > > + if (newpage && PageTransHuge(newpage)) > > thp_migration_success(true); > > put_page(page); > > if (reason == MR_MEMORY_FAILURE) { > > > > Thanks Hugh. I am preparing to respin the vmstat patch accommodating some > earlier comments. Wondering if I should also fold these changes here after > adding your signed-off-by ? Thanks for asking, but please just fold this one-line fixup into your respin without my signed-off-by: I'm not heavily invested in these stats, just want to avoid the crash; and don't know if I would want to sign the result. You could add something like [hughd: fixed oops on NULL newpage] to confirm that the fix is on board, but the fix is what matters. Hugh