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Tue, 20 Oct 2026 23:03:36 -0700 (PDT) Received: from localhost ([2a03:2880:10ff:42::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b1300c85c9sm7295167b3.23.2026.10.20.23.03.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 23:03:34 -0700 (PDT) From: Nhat Pham To: akpm@linux-foundation.org Cc: chrisl@kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, yosry@kernel.org, david@kernel.org, muchun.song@linux.dev, shikemeng@huaweicloud.com, baoquan.he@linux.dev, baohua@kernel.org, youngjun.park@lge.com, chengming.zhou@linux.dev, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, qi.zheng@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, riel@surriel.com, gourry@gourry.net, haowenchao22@gmail.com, corbet@lwn.net, hughd@google.com, baolin.wang@linux.alibaba.com, tj@kernel.org, mkoutny@suse.com, skhan@linuxfoundation.org, rdunlap@infradead.org, kunwu.chan@linux.dev, kernel-team@meta.com, nphamcs@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org Subject: [PATCH v6 03/12] mm, swap: prepare the swap IO path for vswap Date: Tue, 20 Oct 2026 23:03:14 -0700 Message-ID: <20261021060323.553433-4-nphamcs@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261021060323.553433-1-nphamcs@gmail.com> References: <20261021060323.553433-1-nphamcs@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In preparation for adding a physical swap backend for vswap, make the swap IO path able to submit IO for a swap entry other than folio->swap. The swap IO path derives the target device and sector from folio->swap. For a vswap folio backed by a physical slot that entry is virtual, so it identifies neither the backing device nor the sector to submit IO against. Compute the sector from an explicit entry (swap_folio_sector becomes swap_entry_sector), thread that entry through swap_add_folio, __swap_writeout and ops->can_merge, and stash it in swap_iocb so the submit and completion paths address the IO from it rather than from folio->swap. Carry reclaim's NOFS restriction in the I/O context. A subsequent patch uses it when zswap_store() fails and writeout falls back to physical swap. ops->can_merge changes anchor with it: swap_bdev_can_merge() compares sectors and swap_fs_can_merge() byte offsets, and both now measure from the batch head plus the accumulated length instead of from the previous folio plus its size. The two agree at every step, since a batch only grows through merges that passed the same test. The blkg comparison is unchanged and still anchors on the last folio in the batch. All callers pass folio->swap, so there is no functional change. Signed-off-by: Nhat Pham --- include/linux/swap.h | 2 +- include/linux/swap_ops.h | 10 +++++--- mm/page_io.c | 54 +++++++++++++++++++--------------------- mm/swap.h | 3 ++- mm/swapfile.c | 6 ++--- mm/vmscan.c | 4 ++- mm/zswap.c | 2 +- 7 files changed, 42 insertions(+), 39 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 1479914d545d..4066d99f896e 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -414,7 +414,7 @@ extern int __swap_count(swp_entry_t entry); extern bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry); extern int swp_swapcount(swp_entry_t entry); extern struct swap_info_struct *get_swap_device(swp_entry_t entry); -sector_t swap_folio_sector(struct folio *folio); +sector_t swap_entry_sector(swp_entry_t entry); /* * If there is an existing swap slot reference (swap entry) and the caller diff --git a/include/linux/swap_ops.h b/include/linux/swap_ops.h index 57ac6c703f68..1c65e346e127 100644 --- a/include/linux/swap_ops.h +++ b/include/linux/swap_ops.h @@ -12,11 +12,13 @@ struct swap_iocb { struct bio_vec bvecs[SWAP_CLUSTER_MAX]; int nr_bvecs; int len; + swp_entry_t entry; /* first slot in the batch; addresses the IO */ }; struct swap_io_ctx { struct swap_iocb *sio; struct swap_info_struct *sis; + bool nofs; }; /* @@ -30,15 +32,15 @@ struct swap_io_ctx { struct swap_ops { unsigned int flags; - bool (*can_merge)(struct folio *folio, struct folio *prev_folio, - size_t prev_folio_size, int rw); + bool (*can_merge)(struct folio *folio, swp_entry_t phys, + struct swap_iocb *sio, int rw); void (*submit_write)(struct swap_io_ctx *ctx); void (*submit_read)(struct swap_io_ctx *ctx); }; void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter); -bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio, - size_t prev_folio_size, int rw); +bool swap_fs_can_merge(struct folio *folio, swp_entry_t phys, + struct swap_iocb *sio, int rw); int swap_fs_activate(struct swap_info_struct *sis, const struct swap_ops *ops); #endif /* _MM_SWAP_OPS_H */ diff --git a/mm/page_io.c b/mm/page_io.c index f849c285ba22..61bb5c6e9759 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -263,7 +263,7 @@ int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio) return AOP_WRITEPAGE_ACTIVATE; } - __swap_writeout(ctx, folio); + __swap_writeout(ctx, folio, folio->swap); return 0; out_unlock: folio_unlock(folio); @@ -338,24 +338,22 @@ int sio_pool_init(void) } static bool swap_can_merge(struct swap_io_ctx *ctx, struct folio *folio, - int rw) + swp_entry_t phys, int rw) { - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); - struct bio_vec *last_bv = &ctx->sio->bvecs[ctx->sio->nr_bvecs - 1]; - struct folio *prev_folio = bvec_folio(last_bv); - size_t prev_folio_size = folio_size(prev_folio); + struct swap_info_struct *sis = __swap_entry_to_info(phys); if (ctx->sis != sis) return false; - return sis->ops->can_merge(folio, prev_folio, prev_folio_size, rw); + return sis->ops->can_merge(folio, phys, ctx->sio, rw); } -static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw) +static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, + swp_entry_t phys, int rw) { - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); + struct swap_info_struct *sis = __swap_entry_to_info(phys); struct swap_iocb *sio = ctx->sio; - if (sio && !swap_can_merge(ctx, folio, rw)) { + if (sio && !swap_can_merge(ctx, folio, phys, rw)) { if (rw == WRITE) swap_write_submit(ctx); else @@ -368,6 +366,7 @@ static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw) ctx->sio = sio = mempool_alloc(sio_pool, GFP_NOIO); sio->nr_bvecs = 0; sio->len = 0; + sio->entry = phys; } bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0); sio->len += folio_size(folio); @@ -388,7 +387,8 @@ static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw) } } -void __swap_writeout(struct swap_io_ctx *ctx, struct folio *folio) +void __swap_writeout(struct swap_io_ctx *ctx, struct folio *folio, + swp_entry_t phys) { VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio); @@ -404,7 +404,7 @@ void __swap_writeout(struct swap_io_ctx *ctx, struct folio *folio) folio_start_writeback(folio); folio_unlock(folio); - swap_add_folio(ctx, folio, WRITE); + swap_add_folio(ctx, folio, phys, WRITE); } /* @@ -508,7 +508,7 @@ void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio) /* We have to read from slower devices. Increase zswap protection. */ zswap_folio_swapin(folio); - swap_add_folio(ctx, folio, READ); + swap_add_folio(ctx, folio, folio->swap, READ); finish: if (workingset) { @@ -540,8 +540,6 @@ static void swap_fs_write_complete(struct kiocb *iocb, long ret) bool failed = ret != sio->len; if (failed) { - struct folio *folio = bvec_folio(&sio->bvecs[0]); - /* * In the case of swap-over-nfs, this can be a temporary failure * if the system has limited memory for allocating transmit @@ -549,7 +547,7 @@ static void swap_fs_write_complete(struct kiocb *iocb, long ret) * folio_rotate_reclaimable but rate-limit the messages. */ pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n", - ret, swap_dev_pos(folio->swap)); + ret, swap_dev_pos(sio->entry)); } swap_write_end(sio, failed); @@ -621,7 +619,7 @@ static void swap_bdev_submit_write(struct swap_io_ctx *ctx) bio_init(bio, ctx->sis->bdev, sio->bvecs, ARRAY_SIZE(sio->bvecs), REQ_OP_WRITE | REQ_SWAP); bio->bi_iter.bi_size = sio->len; - bio->bi_iter.bi_sector = swap_folio_sector(bio_first_folio_all(bio)); + bio->bi_iter.bi_sector = swap_entry_sector(sio->entry); bio_associate_blkg_from_folio(bio, bio_first_folio_all(bio)); if (ctx->sis->flags & SWP_SYNCHRONOUS_IO) { @@ -650,7 +648,7 @@ static void swap_bdev_submit_read(struct swap_io_ctx *ctx) bio_init(bio, ctx->sis->bdev, sio->bvecs, ARRAY_SIZE(sio->bvecs), REQ_OP_READ); bio->bi_iter.bi_size = sio->len; - bio->bi_iter.bi_sector = swap_folio_sector(bio_first_folio_all(bio)); + bio->bi_iter.bi_sector = swap_entry_sector(sio->entry); if (ctx->sis->flags & SWP_SYNCHRONOUS_IO) { /* @@ -668,13 +666,14 @@ static void swap_bdev_submit_read(struct swap_io_ctx *ctx) } } -static bool swap_bdev_can_merge(struct folio *folio, struct folio *prev_folio, - size_t prev_folio_size, int rw) +static bool swap_bdev_can_merge(struct folio *folio, swp_entry_t phys, + struct swap_iocb *sio, int rw) { - if (swap_folio_sector(folio) != - swap_folio_sector(prev_folio) + (prev_folio_size >> SECTOR_SHIFT)) + if (swap_entry_sector(phys) != + swap_entry_sector(sio->entry) + (sio->len >> SECTOR_SHIFT)) return false; - if (rw == WRITE && !folio_blkg_can_merge(folio, prev_folio)) + if (rw == WRITE && !folio_blkg_can_merge(folio, + bvec_folio(&sio->bvecs[sio->nr_bvecs - 1]))) return false; return true; } @@ -690,7 +689,7 @@ void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter) struct swap_iocb *sio = ctx->sio; init_sync_kiocb(&sio->iocb, ctx->sis->swap_file); - sio->iocb.ki_pos = swap_dev_pos(bvec_folio(&sio->bvecs[0])->swap); + sio->iocb.ki_pos = swap_dev_pos(sio->entry); if (rw == WRITE) sio->iocb.ki_complete = swap_fs_write_complete; else @@ -701,11 +700,10 @@ void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter) } EXPORT_SYMBOL_GPL(swap_fs_prepare_rw); -bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio, - size_t prev_folio_size, int rw) +bool swap_fs_can_merge(struct folio *folio, swp_entry_t phys, + struct swap_iocb *sio, int rw) { - return swap_dev_pos(folio->swap) == - swap_dev_pos(prev_folio->swap) + prev_folio_size; + return swap_dev_pos(phys) == swap_dev_pos(sio->entry) + sio->len; } EXPORT_SYMBOL_GPL(swap_fs_can_merge); diff --git a/mm/swap.h b/mm/swap.h index d0e7c991a4c0..b0a092b47fce 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -320,7 +320,8 @@ void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio); void swap_read_submit(struct swap_io_ctx *ctx); void swap_write_submit(struct swap_io_ctx *ctx); int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio); -void __swap_writeout(struct swap_io_ctx *ctx, struct folio *folio); +void __swap_writeout(struct swap_io_ctx *ctx, struct folio *folio, + swp_entry_t phys); /* linux/mm/swap_state.c */ extern struct address_space swap_space __read_mostly; diff --git a/mm/swapfile.c b/mm/swapfile.c index 81ac45b4856e..69fac2d905a4 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -341,14 +341,14 @@ offset_to_swap_extent(struct swap_info_struct *sis, unsigned long offset) BUG(); } -sector_t swap_folio_sector(struct folio *folio) +sector_t swap_entry_sector(swp_entry_t entry) { - struct swap_info_struct *sis = __swap_entry_to_info(folio->swap); + struct swap_info_struct *sis = __swap_entry_to_info(entry); struct swap_extent *se; sector_t sector; pgoff_t offset; - offset = swp_offset(folio->swap); + offset = swp_offset(entry); se = offset_to_swap_extent(sis, offset); sector = se->start_block + (offset - se->start_page); return sector << (PAGE_SHIFT - 9); diff --git a/mm/vmscan.c b/mm/vmscan.c index 4c5f0f97c1c7..b9c5e92757f3 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1172,7 +1172,9 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, unsigned int nr_reclaimed = 0, nr_demoted = 0; unsigned int pgactivate = 0; bool do_demote_pass; - struct swap_io_ctx ctx = {}; + struct swap_io_ctx ctx = { + .nofs = !(sc->gfp_mask & __GFP_FS), + }; folio_batch_init(&free_folios); memset(stat, 0, sizeof(*stat)); diff --git a/mm/zswap.c b/mm/zswap.c index 1ba191cbc26f..73c6b82aa593 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -1159,7 +1159,7 @@ static int zswap_writeback_entry(struct zswap_entry *entry, folio_put(folio); /* start writeback */ - __swap_writeout(&ctx, folio); + __swap_writeout(&ctx, folio, folio->swap); swap_write_submit(&ctx); return 0; -- 2.53.0-Meta