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[2003:d8:2f06:a600:a397:de1d:2f8b:b66f]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-459fb43b491sm120611835e9.3.2025.08.11.07.39.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Aug 2025 07:39:54 -0700 (PDT) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-btrfs@vger.kernel.org, jfs-discussion@lists.sourceforge.net, David Hildenbrand , Andrew Morton , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Jerrin Shaji George , Arnd Bergmann , Greg Kroah-Hartman , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?q?Eugenio=20P=C3=A9rez?= , Alexander Viro , Christian Brauner , Jan Kara , Benjamin LaHaise , Chris Mason , Josef Bacik , David Sterba , Muchun Song , Oscar Salvador , Dave Kleikamp , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Minchan Kim , Sergey Senozhatsky Subject: [PATCH v1 1/2] mm/migrate: remove MIGRATEPAGE_UNMAP Date: Mon, 11 Aug 2025 16:39:47 +0200 Message-ID: <20250811143949.1117439-2-david@redhat.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250811143949.1117439-1-david@redhat.com> References: <20250811143949.1117439-1-david@redhat.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Y9kMzKDqmRRkFIu17oZpHs0Hz88D58L_yaXq49CxpLg_1754923195 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true migrate_folio_unmap() is the only user of MIGRATEPAGE_UNMAP. We want to remove MIGRATEPAGE_* completely. It's rather weird to have a generic MIGRATEPAGE_UNMAP, documented to be returned from address-space callbacks, when it's only used for an internal helper. Let's start by having only a single "success" return value for migrate_folio_unmap() -- 0 -- by moving the "folio was already freed" check into the single caller. There is a remaining comment for PG_isolated, which we renamed to PG_movable_ops_isolated recently and forgot to update. While we might still run into that case with zsmalloc, it's something we want to get rid of soon. So let's just focus that optimization on real folios only for now by excluding movable_ops pages. Note that concurrent freeing can happen at any time and this "already freed" check is not relevant for correctness. Signed-off-by: David Hildenbrand --- include/linux/migrate.h | 1 - mm/migrate.c | 40 ++++++++++++++++++++-------------------- 2 files changed, 20 insertions(+), 21 deletions(-) diff --git a/include/linux/migrate.h b/include/linux/migrate.h index acadd41e0b5cf..40f2b5a37efbb 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -18,7 +18,6 @@ struct migration_target_control; * - zero on page migration success; */ #define MIGRATEPAGE_SUCCESS 0 -#define MIGRATEPAGE_UNMAP 1 /** * struct movable_operations - Driver page migration diff --git a/mm/migrate.c b/mm/migrate.c index 425401b2d4e14..e9dacf1028dc7 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1176,16 +1176,6 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, bool locked = false; bool dst_locked = false; - if (folio_ref_count(src) == 1) { - /* Folio was freed from under us. So we are done. */ - folio_clear_active(src); - folio_clear_unevictable(src); - /* free_pages_prepare() will clear PG_isolated. */ - list_del(&src->lru); - migrate_folio_done(src, reason); - return MIGRATEPAGE_SUCCESS; - } - dst = get_new_folio(src, private); if (!dst) return -ENOMEM; @@ -1275,7 +1265,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, if (unlikely(page_has_movable_ops(&src->page))) { __migrate_folio_record(dst, old_page_state, anon_vma); - return MIGRATEPAGE_UNMAP; + return 0; } /* @@ -1305,7 +1295,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, if (!folio_mapped(src)) { __migrate_folio_record(dst, old_page_state, anon_vma); - return MIGRATEPAGE_UNMAP; + return 0; } out: @@ -1848,14 +1838,28 @@ static int migrate_pages_batch(struct list_head *from, continue; } + /* + * If we are holding the last folio reference, the folio + * was freed from under us, so just drop our reference. + */ + if (likely(!page_has_movable_ops(&folio->page)) && + folio_ref_count(folio) == 1) { + folio_clear_active(folio); + folio_clear_unevictable(folio); + list_del(&folio->lru); + migrate_folio_done(folio, reason); + stats->nr_succeeded += nr_pages; + stats->nr_thp_succeeded += is_thp; + continue; + } + rc = migrate_folio_unmap(get_new_folio, put_new_folio, private, folio, &dst, mode, reason, ret_folios); /* * The rules are: - * Success: folio will be freed - * Unmap: folio will be put on unmap_folios list, - * dst folio put on dst_folios list + * 0: folio will be put on unmap_folios list, + * dst folio put on dst_folios list * -EAGAIN: stay on the from list * -ENOMEM: stay on the from list * Other errno: put on ret_folios list @@ -1905,11 +1909,7 @@ static int migrate_pages_batch(struct list_head *from, thp_retry += is_thp; nr_retry_pages += nr_pages; break; - case MIGRATEPAGE_SUCCESS: - stats->nr_succeeded += nr_pages; - stats->nr_thp_succeeded += is_thp; - break; - case MIGRATEPAGE_UNMAP: + case 0: list_move_tail(&folio->lru, &unmap_folios); list_add_tail(&dst->lru, &dst_folios); break; -- 2.50.1