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Sat, 28 Mar 2026 00:58:34 -0700 (PDT) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: bhe@redhat.com, baohua@kernel.org, chrisl@kernel.org, kasong@tencent.com, nphamcs@gmail.com, shikemeng@huaweicloud.com, youngjun.park@lge.com, linux-kernel@vger.kernel.org Subject: [PATCH v2 2/3] mm/swap: use swap_ops to register swap device's methods Date: Sat, 28 Mar 2026 15:58:11 +0800 Message-Id: <20260328075812.11060-3-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20260328075812.11060-1-21cnbao@gmail.com> References: <20260328075812.11060-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Baoquan He 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 Signed-off-by: Baoquan He Co-developed-by: Barry Song Signed-off-by: Barry Song --- include/linux/swap.h | 2 + mm/swap.h | 10 ++++- mm/swap_io.c | 99 +++++++++++++++++++++++++------------------- mm/swapfile.c | 1 + mm/zswap.c | 3 +- 5 files changed, 70 insertions(+), 45 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 1930f81e6be4..b52f30dad72b 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 */ }; =20 +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; }; =20 static inline swp_entry_t page_swap_entry(struct page *page) diff --git a/mm/swap.h b/mm/swap.h index 161185057993..219dbcb3ffb1 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -217,6 +217,15 @@ extern void __swap_cluster_free_entries(struct swap_in= fo_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); +}; +void setup_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 *p= lug) } 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); =20 /* 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 91b33d955e63..ad0895af6ed8 100644 --- a/mm/swap_io.c +++ b/mm/swap_io.c @@ -238,6 +238,7 @@ static void swap_zeromap_folio_clear(struct folio *foli= o) int swap_writeout(struct folio *folio, struct swap_iocb **swap_plug) { int ret =3D 0; + struct swap_info_struct *sis =3D __swap_entry_to_info(folio->swap); =20 if (folio_free_swap(folio)) goto out_unlock; @@ -283,7 +284,8 @@ int swap_writeout(struct folio *folio, struct swap_iocb= **swap_plug) } rcu_read_unlock(); =20 - __swap_writepage(folio, swap_plug); + VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio); + sis->ops->write_folio(sis, folio, swap_plug); return 0; out_unlock: folio_unlock(folio); @@ -373,10 +375,11 @@ static void sio_write_complete(struct kiocb *iocb, lo= ng ret) mempool_free(sio, sio_pool); } =20 -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 =3D swap_plug ? *swap_plug : NULL; - struct swap_info_struct *sis =3D __swap_entry_to_info(folio->swap); struct file *swap_file =3D sis->swap_file; loff_t pos =3D swap_dev_pos(folio->swap); =20 @@ -409,8 +412,9 @@ static void swap_writepage_fs(struct folio *folio, stru= ct swap_iocb **swap_plug) *swap_plug =3D sio; } =20 -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 +433,9 @@ static void swap_writepage_bdev_sync(struct folio *foli= o, __end_swap_bio_write(&bio); } =20 -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; =20 @@ -446,29 +451,6 @@ static void swap_writepage_bdev_async(struct folio *fo= lio, submit_bio(bio); } =20 -void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug) -{ - struct swap_info_struct *sis =3D __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 +519,10 @@ static bool swap_read_folio_zeromap(struct folio *foli= o) return true; } =20 -static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plu= g) +static void swap_read_folio_fs(struct swap_info_struct *sis, + struct folio *folio, + struct swap_iocb **plug) { - struct swap_info_struct *sis =3D __swap_entry_to_info(folio->swap); struct swap_iocb *sio =3D NULL; loff_t pos =3D swap_dev_pos(folio->swap); =20 @@ -571,8 +554,9 @@ static void swap_read_folio_fs(struct folio *folio, str= uct swap_iocb **plug) *plug =3D sio; } =20 -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 +577,9 @@ static void swap_read_folio_bdev_sync(struct folio *fol= io, put_task_struct(current); } =20 -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; =20 @@ -608,6 +593,39 @@ static void swap_read_folio_bdev_async(struct folio *f= olio, submit_bio(bio); } =20 +static const struct swap_ops bdev_fs_swap_ops =3D { + .read_folio =3D swap_read_folio_fs, + .write_folio =3D swap_writepage_fs, +}; + +static const struct swap_ops bdev_sync_swap_ops =3D { + .read_folio =3D swap_read_folio_bdev_sync, + .write_folio =3D swap_writepage_bdev_sync, +}; + +static const struct swap_ops bdev_async_swap_ops =3D { + .read_folio =3D swap_read_folio_bdev_async, + .write_folio =3D swap_writepage_bdev_async, +}; + +void setup_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 =3D &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 =3D &bdev_sync_swap_ops; + else + sis->ops =3D &bdev_async_swap_ops; +} + void swap_read_folio(struct folio *folio, struct swap_iocb **plug) { struct swap_info_struct *sis =3D __swap_entry_to_info(folio->swap); @@ -642,13 +660,8 @@ 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); =20 - 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); - } + VM_WARN_ON_ONCE(!sis->ops || !sis->ops->read_folio); + sis->ops->read_folio(sis, folio, plug); =20 finish: if (workingset) { diff --git a/mm/swapfile.c b/mm/swapfile.c index ff315b752afd..c9eb95141c8f 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -3732,6 +3732,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialf= ile, int, swap_flags) si->list.prio =3D -si->prio; si->avail_list.prio =3D -si->prio; si->swap_file =3D swap_file; + setup_swap_ops(si); =20 /* Sets SWP_WRITEOK, resurrect the percpu ref, expose the swap device */ enable_swap_info(si); diff --git a/mm/zswap.c b/mm/zswap.c index 4b5149173b0e..9bacb1733e1c 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -1054,7 +1054,8 @@ static int zswap_writeback_entry(struct zswap_entry *= entry, folio_set_reclaim(folio); =20 /* start writeback */ - __swap_writepage(folio, NULL); + VM_WARN_ON_ONCE(!sis->ops || !sis->ops->write_folio); + si->ops->write_folio(si, folio, NULL); =20 out: if (ret && ret !=3D -EEXIST) { --=20 2.39.3 (Apple Git-146)