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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1778582544; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=e2j1qUAZVyouu0JkJWti5wQaqLNp7X4s2VzEYi23lW8=; b=f5eBltfkS8d+d9iJtUvnk6re1hfqHc6W/UuKelt5rv8HK9dvTTKHxU07Bqizvs+bVNussc 5jbkgNmGmHGIeH34gWCoRTNfP9F1lgB4dVBni5ZHk6CW6u1+14yOScG7x4ylSb78CEby+3 wwfGjIU0BC1aYK00DJ1IBUqj6O51WAg= From: Baoquan He To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, chrisl@kernel.org, usama.arif@linux.dev, baohua@kernel.org, kasong@tencent.com, nphamcs@gmail.com, shikemeng@huaweicloud.com, youngjun.park@lge.com, linux-kernel@vger.kernel.org, Baoquan He Subject: [PATCH v6 2/3] mm/swap: use swap_ops to register swap device's methods Date: Tue, 12 May 2026 18:42:00 +0800 Message-ID: <20260512104201.716213-3-baoquan.he@linux.dev> In-Reply-To: <20260512104201.716213-1-baoquan.he@linux.dev> References: <20260512104201.716213-1-baoquan.he@linux.dev> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 7A219C0004 X-Rspamd-Server: rspam06 X-Stat-Signature: ye51onr65r69t5sae8bfg6uy4gkj7dtu X-HE-Tag: 1778582545-759870 X-HE-Meta: U2FsdGVkX1+9UgYoIQeh+YG4P0y7duIWYPx1U9ee12Fc6sxmf+Xcdc3PqNGP70F/HRBdQqRAWos8tjYOMffd/7oZWsbu+mLxdT9aCljfHB1tlM2uYmZnsEHRzGJFAAexKYAJV4HNKMoSYEQ5Ibl1rn5BVXdsmfYgRzDcClZLx/bbVFRFzvBu0/g3S49MFelkzzsaiBB+TXdRyfYgC5w8ci6O3jtlH43Bt5ttcyo88rchuy6PgBRLhBhfzBMuoWC03IUkPs6CM+FTlmslNz+pqlf3jXu+yyVYwon9hwsgJb6eLecEZ73dErAlH6M1PNgcJYGxOqbT9IEzKwdTXi1UOe+SGS9R8Lqw49vXaYYhCGLiTp90vyhqHYTNdqyPGwqD4wQ8YwZRWCxrousZJXjbH/i/uQVxFH6+NBXrNRb65pr4q0bSV340R5AF8kch3P9l+OWQ4ZAFoqyVcQbKwB9cjILBZsa2bdh+W0vHBIsmbXFJCYNNiSv5KOzzrwfYAMgxvT8dSzoE4VyMC3DFJ9vI4FYPUGtKG0x274goCjn3PDuIK8BrkAyohV048585qFcYN76jHY53q1lnJuGxH2KKrosN/lNDnKfg2t38pzxWRptCZGs4ADYUjcLzUE3+mq+GA1mKWEeyIrJMQriJiNf4fQg3/fS8vPltQHQjajrtcT5MuSJOI5kwaGllDh2MObVrzxIGaELaWMmSbxOPaGjVuOqdzeWgobTydC6PAESPCrTcCILHMLi0AO/D3h4BKZUUstCW/qcO59t01qGj8Y6T6VTl3TmquhZWMtI/Ewa2bcxXwj0vhzAyfJXcMQaCw0LdOnC+Rn92zfCqwYx8QeOMJlXAXCSOY0Bul8faZtM18HXguZnF2VxMirSNCJfOsQyEcMG4fQ8GqOe8mFXawiqQDvETP39JAw7nWFy8FCgAQ/WAIHGgFoNHGsXsGpgo9Ro/8/1tjh2PGhSIEkQr2r0 TjNaHrO0 maee3Lyrr06BtGhz3nK39UoPb8ru2dbTpLzrx/Xr8NNhjnVEGWqeJ/tRFWOjKCZG7uwiGkTcA9QoFQ54QAtI6w0pCyvDPlYizJb7hOVsLRY8FsRJ5LMSBo2f4tTWX8mCEGnWESWmtu1ahc++xNtM4tfFUWzfn88w8tAktAnOW1GRXq2/kH4BRB9q+bNQSYdra5JSUAxKmRwjPdi7mfozr+29/71ghrhz6f2Jx1qRAMidwcoSU/nB6ak9zePkh1TsvPBCU8k52K4VTe7I= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: This simplifies codes and makes logic clearer. And also makes later any new swap device type being added easier to handle. Currently there are three types of swap devices: bdev_fs, bdev_sync and bdev_async, and only operations read_folio and write_folio are included. In the future, there could be more swap device types added and more appropriate opeations adapted into swap_ops. Suggested-by: Chris Li Acked-by: Chris Li Co-developed-by: Barry Song Signed-off-by: Barry Song Signed-off-by: Baoquan He --- include/linux/swap.h | 2 + mm/swap.h | 10 ++++- mm/swap_io.c | 102 +++++++++++++++++++++++++------------------ mm/swapfile.c | 9 ++++ mm/zswap.c | 2 +- 5 files changed, 80 insertions(+), 45 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index aa89e1d30a77..85f15ec326c1 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -243,6 +243,7 @@ struct swap_sequential_cluster { unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */ }; +struct swap_ops; /* * The in-memory structure used to track swap areas. */ @@ -283,6 +284,7 @@ struct swap_info_struct { struct work_struct reclaim_work; /* reclaim worker */ struct list_head discard_clusters; /* discard clusters list */ struct plist_node avail_list; /* entry in swap_avail_head */ + const struct swap_ops *ops; }; static inline swp_entry_t page_swap_entry(struct page *page) diff --git a/mm/swap.h b/mm/swap.h index 161185057993..29bdc679fa98 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -217,6 +217,15 @@ extern void __swap_cluster_free_entries(struct swap_info_struct *si, /* linux/mm/swap_io.c */ int sio_pool_init(void); struct swap_iocb; +struct swap_ops { + void (*read_folio)(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug); + void (*write_folio)(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug); +}; +int init_swap_ops(struct swap_info_struct *sis); void swap_read_folio(struct folio *folio, struct swap_iocb **plug); void __swap_read_unplug(struct swap_iocb *plug); static inline void swap_read_unplug(struct swap_iocb *plug) @@ -226,7 +235,6 @@ static inline void swap_read_unplug(struct swap_iocb *plug) } void swap_write_unplug(struct swap_iocb *sio); int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug); -void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug); /* linux/mm/swap_state.c */ extern struct address_space swap_space __read_mostly; diff --git a/mm/swap_io.c b/mm/swap_io.c index 7c1a3a3a53f8..3f9aee5b6a4d 100644 --- a/mm/swap_io.c +++ b/mm/swap_io.c @@ -238,6 +238,7 @@ static void swap_zeromap_folio_clear(struct folio *folio) int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug) { int ret = 0; + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); if (folio_free_swap(folio)) goto out_unlock; @@ -283,7 +284,7 @@ int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug) } rcu_read_unlock(); - __swap_writepage(folio, swap_plug); + sis->ops->write_folio(sis, folio, swap_plug); return 0; out_unlock: folio_unlock(folio); @@ -373,10 +374,11 @@ static void sio_write_complete(struct kiocb *iocb, long ret) mempool_free(sio, sio_pool); } -static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug) +static void swap_writepage_fs(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **swap_plug) { struct swap_iocb *sio = swap_plug ? *swap_plug : NULL; - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); struct file *swap_file = sis->swap_file; loff_t pos = swap_dev_pos(folio->swap); @@ -409,8 +411,9 @@ static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug) *swap_plug = sio; } -static void swap_writepage_bdev_sync(struct folio *folio, - struct swap_info_struct *sis) +static void swap_writepage_bdev_sync(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug) { struct bio_vec bv; struct bio bio; @@ -429,8 +432,9 @@ static void swap_writepage_bdev_sync(struct folio *folio, __end_swap_bio_write(&bio); } -static void swap_writepage_bdev_async(struct folio *folio, - struct swap_info_struct *sis) +static void swap_writepage_bdev_async(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug) { struct bio *bio; @@ -446,29 +450,6 @@ static void swap_writepage_bdev_async(struct folio *folio, submit_bio(bio); } -void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug) -{ - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); - - VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio); - /* - * ->flags can be updated non-atomically, - * but that will never affect SWP_FS_OPS, so the data_race - * is safe. - */ - if (data_race(sis->flags & SWP_FS_OPS)) - swap_writepage_fs(folio, swap_plug); - /* - * ->flags can be updated non-atomically, - * but that will never affect SWP_SYNCHRONOUS_IO, so the data_race - * is safe. - */ - else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO)) - swap_writepage_bdev_sync(folio, sis); - else - swap_writepage_bdev_async(folio, sis); -} - void swap_write_unplug(struct swap_iocb *sio) { struct iov_iter from; @@ -537,9 +518,10 @@ static bool swap_read_folio_zeromap(struct folio *folio) return true; } -static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug) +static void swap_read_folio_fs(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug) { - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); struct swap_iocb *sio = NULL; loff_t pos = swap_dev_pos(folio->swap); @@ -571,8 +553,9 @@ static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug) *plug = sio; } -static void swap_read_folio_bdev_sync(struct folio *folio, - struct swap_info_struct *sis) +static void swap_read_folio_bdev_sync(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug) { struct bio_vec bv; struct bio bio; @@ -593,8 +576,9 @@ static void swap_read_folio_bdev_sync(struct folio *folio, put_task_struct(current); } -static void swap_read_folio_bdev_async(struct folio *folio, - struct swap_info_struct *sis) +static void swap_read_folio_bdev_async(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug) { struct bio *bio; @@ -608,6 +592,44 @@ static void swap_read_folio_bdev_async(struct folio *folio, submit_bio(bio); } +static const struct swap_ops bdev_fs_swap_ops = { + .read_folio = swap_read_folio_fs, + .write_folio = swap_writepage_fs, +}; + +static const struct swap_ops bdev_sync_swap_ops = { + .read_folio = swap_read_folio_bdev_sync, + .write_folio = swap_writepage_bdev_sync, +}; + +static const struct swap_ops bdev_async_swap_ops = { + .read_folio = swap_read_folio_bdev_async, + .write_folio = swap_writepage_bdev_async, +}; + +int init_swap_ops(struct swap_info_struct *sis) +{ + /* + * ->flags can be updated non-atomically, but that will + * never affect SWP_FS_OPS, so the data_race is safe. + */ + if (data_race(sis->flags & SWP_FS_OPS)) + sis->ops = &bdev_fs_swap_ops; + /* + * ->flags can be updated non-atomically, but that will + * never affect SWP_SYNCHRONOUS_IO, so the data_race is safe. + */ + else if (data_race(sis->flags & SWP_SYNCHRONOUS_IO)) + sis->ops = &bdev_sync_swap_ops; + else + sis->ops = &bdev_async_swap_ops; + + if (!sis->ops || !sis->ops->read_folio || !sis->ops->write_folio) + return -EINVAL; + + return 0; +} + void swap_read_folio(struct folio *folio, struct swap_iocb **plug) { struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); @@ -642,13 +664,7 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug) /* We have to read from slower devices. Increase zswap protection. */ zswap_folio_swapin(folio); - if (data_race(sis->flags & SWP_FS_OPS)) { - swap_read_folio_fs(folio, plug); - } else if (synchronous) { - swap_read_folio_bdev_sync(folio, sis); - } else { - swap_read_folio_bdev_async(folio, sis); - } + sis->ops->read_folio(sis, folio, plug); finish: if (workingset) { diff --git a/mm/swapfile.c b/mm/swapfile.c index 4840fd40f36f..8c42632e6765 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -3780,6 +3780,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) goto free_swap_zswap; } + /* + * init_swap_ops() sets si->ops based on flags. It does not need + * swapon_mutex, and must complete before enable_swap_info() + * exposes the device. + */ + error = init_swap_ops(si); + if (error) + goto bad_swap_unlock_inode; + mutex_lock(&swapon_mutex); prio = DEF_SWAP_PRIO; if (swap_flags & SWAP_FLAG_PREFER) diff --git a/mm/zswap.c b/mm/zswap.c index 4b5149173b0e..192401f46de4 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -1054,7 +1054,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry, folio_set_reclaim(folio); /* start writeback */ - __swap_writepage(folio, NULL); + si->ops->write_folio(si, folio, NULL); out: if (ret && ret != -EEXIST) { -- 2.52.0