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[73.93.239.127]) by smtp.gmail.com with ESMTPSA id fw24sm3069345pjb.21.2021.04.13.14.24.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Apr 2021 14:24:40 -0700 (PDT) From: Yang Shi To: mgorman@suse.de, kirill.shutemov@linux.intel.com, ziy@nvidia.com, mhocko@suse.com, ying.huang@intel.com, hughd@google.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, akpm@linux-foundation.org Cc: shy828301@gmail.com, linux-mm@kvack.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [v2 PATCH 6/7] mm: migrate: check mapcount for THP instead of ref count Date: Tue, 13 Apr 2021 14:24:15 -0700 Message-Id: <20210413212416.3273-7-shy828301@gmail.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210413212416.3273-1-shy828301@gmail.com> References: <20210413212416.3273-1-shy828301@gmail.com> MIME-Version: 1.0 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D37BFC0007C1 X-Stat-Signature: hcmq5uzu7ssi6yqzcs357q9kbmiwxb3m Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf22; identity=mailfrom; envelope-from=""; helo=mail-pg1-f179.google.com; client-ip=209.85.215.179 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618349078-276130 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The generic migration path will check refcount, so no need check refcount= here. But the old code actually prevents from migrating shared THP (mapped by m= ultiple processes), so bail out early if mapcount is > 1 to keep the behavior. Signed-off-by: Yang Shi --- mm/migrate.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index a72994c68ec6..dc7cc7f3a124 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -2067,6 +2067,10 @@ static int numamigrate_isolate_page(pg_data_t *pgd= at, struct page *page) =20 VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page); =20 + /* Do not migrate THP mapped by multiple processes */ + if (PageTransHuge(page) && page_mapcount(page) > 1) + return 0; + /* Avoid migrating to a node that is nearly full */ if (!migrate_balanced_pgdat(pgdat, compound_nr(page))) return 0; @@ -2074,18 +2078,6 @@ static int numamigrate_isolate_page(pg_data_t *pgd= at, struct page *page) if (isolate_lru_page(page)) return 0; =20 - /* - * migrate_misplaced_transhuge_page() skips page migration's usual - * check on page_count(), so we must do it here, now that the page - * has been isolated: a GUP pin, or any other pin, prevents migration. - * The expected page count is 3: 1 for page's mapcount and 1 for the - * caller's pin and 1 for the reference taken by isolate_lru_page(). - */ - if (PageTransHuge(page) && page_count(page) !=3D 3) { - putback_lru_page(page); - return 0; - } - page_lru =3D page_is_file_lru(page); mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru, thp_nr_pages(page)); --=20 2.26.2