diff --git a/include/linux/swap.h b/include/linux/swap.h index 248db1dd7812..ca533b478c21 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -296,6 +296,7 @@ struct swap_info_struct { signed char type; /* strange name for an index */ unsigned int max; /* extent of the swap_map */ unsigned char *swap_map; /* vmalloc'ed array of usage counts */ + unsigned long *zeromap; /* kvmalloc'ed bitmap to track zero pages */ struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */ struct list_head free_clusters; /* free clusters list */ struct list_head full_clusters; /* full clusters list */ diff --git a/mm/page_io.c b/mm/page_io.c index a00e2f615118..b6f1519d63b0 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -172,6 +172,80 @@ bad_bmap: goto out; } +static bool is_folio_zero_filled(struct folio *folio) +{ + unsigned int pos, last_pos; + unsigned long *data; + unsigned int i; + + last_pos = PAGE_SIZE / sizeof(*data) - 1; + for (i = 0; i < folio_nr_pages(folio); i++) { + data = kmap_local_folio(folio, i * PAGE_SIZE); + /* + * Check last word first, incase the page is zero-filled at + * the start and has non-zero data at the end, which is common + * in real-world workloads. + */ + if (data[last_pos]) { + kunmap_local(data); + return false; + } + for (pos = 0; pos < last_pos; pos++) { + if (data[pos]) { + kunmap_local(data); + return false; + } + } + kunmap_local(data); + } + + return true; +} + +static void swap_zeromap_folio_set(struct folio *folio) +{ + struct swap_info_struct *sis = swp_swap_info(folio->swap); + swp_entry_t entry; + unsigned int i; + + for (i = 0; i < folio_nr_pages(folio); i++) { + entry = page_swap_entry(folio_page(folio, i)); + set_bit(swp_offset(entry), sis->zeromap); + } +} + +static void swap_zeromap_folio_clear(struct folio *folio) +{ + struct swap_info_struct *sis = swp_swap_info(folio->swap); + swp_entry_t entry; + unsigned int i; + + for (i = 0; i < folio_nr_pages(folio); i++) { + entry = page_swap_entry(folio_page(folio, i)); + clear_bit(swp_offset(entry), sis->zeromap); + } +} + +/* + * Return the index of the first subpage which is not zero-filled + * according to swap_info_struct->zeromap. + * If all pages are zero-filled according to zeromap, it will return + * folio_nr_pages(folio). + */ +static unsigned int swap_zeromap_folio_test(struct folio *folio) +{ + struct swap_info_struct *sis = swp_swap_info(folio->swap); + swp_entry_t entry; + unsigned int i; + + for (i = 0; i < folio_nr_pages(folio); i++) { + entry = page_swap_entry(folio_page(folio, i)); + if (!test_bit(swp_offset(entry), sis->zeromap)) + return i; + } + return i; +} + /* * We may have stale swap cache pages in memory: notice * them here and get rid of the unnecessary final write. @@ -195,6 +269,25 @@ int swap_writepage(struct page *page, struct writeback_control *wbc) folio_unlock(folio); return ret; } + + /* + * Use a bitmap (zeromap) to avoid doing IO for zero-filled pages. + * The bits in zeromap are protected by the locked swapcache folio + * and atomic updates are used to protect against read-modify-write + * corruption due to other zero swap entries seeing concurrent updates. + */ + if (is_folio_zero_filled(folio)) { + swap_zeromap_folio_set(folio); + folio_unlock(folio); + return 0; + } else { + /* + * Clear bits this folio occupies in the zeromap to prevent + * zero data being read in from any previous zero writes that + * occupied the same swap entries. + */ + swap_zeromap_folio_clear(folio); + } if (zswap_store(folio)) { folio_unlock(folio); return 0; @@ -427,6 +520,26 @@ static void sio_read_complete(struct kiocb *iocb, long ret) mempool_free(sio, sio_pool); } +static bool swap_read_folio_zeromap(struct folio *folio) +{ + unsigned int idx = swap_zeromap_folio_test(folio); + + if (idx == 0) + return false; + + /* + * Swapping in a large folio that is partially in the zeromap is not + * currently handled. Return true without marking the folio uptodate so + * that an IO error is emitted (e.g. do_swap_page() will sigbus). + */ + if (WARN_ON_ONCE(idx < folio_nr_pages(folio))) + return true; + + folio_zero_range(folio, 0, folio_size(folio)); + folio_mark_uptodate(folio); + return true; +} + static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug) { struct swap_info_struct *sis = swp_swap_info(folio->swap); @@ -517,7 +630,10 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug) } delayacct_swapin_start(); - if (zswap_load(folio)) { + if (swap_read_folio_zeromap(folio)) { + folio_unlock(folio); + goto finish; + } else if (zswap_load(folio)) { folio_unlock(folio); goto finish; } diff --git a/mm/swapfile.c b/mm/swapfile.c index 03dc77457510..8e317c495bfb 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -940,6 +940,14 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset, unsigned long begin = offset; unsigned long end = offset + nr_entries - 1; void (*swap_slot_free_notify)(struct block_device *, unsigned long); + unsigned int i; + + /* + * Use atomic clear_bit operations only on zeromap instead of non-atomic + * bitmap_clear to prevent adjacent bits corruption due to simultaneous writes. + */ + for (i = 0; i < nr_entries; i++) + clear_bit(offset + i, si->zeromap); if (offset < si->lowest_bit) si->lowest_bit = offset; @@ -2609,7 +2617,8 @@ static int swap_node(struct swap_info_struct *si) static void setup_swap_info(struct swap_info_struct *si, int prio, unsigned char *swap_map, - struct swap_cluster_info *cluster_info) + struct swap_cluster_info *cluster_info, + unsigned long *zeromap) { int i; @@ -2634,6 +2643,7 @@ static void setup_swap_info(struct swap_info_struct *si, int prio, } si->swap_map = swap_map; si->cluster_info = cluster_info; + si->zeromap = zeromap; } static void _enable_swap_info(struct swap_info_struct *si) @@ -2662,11 +2672,12 @@ static void _enable_swap_info(struct swap_info_struct *si) static void enable_swap_info(struct swap_info_struct *si, int prio, unsigned char *swap_map, - struct swap_cluster_info *cluster_info) + struct swap_cluster_info *cluster_info, + unsigned long *zeromap) { spin_lock(&swap_lock); spin_lock(&si->lock); - setup_swap_info(si, prio, swap_map, cluster_info); + setup_swap_info(si, prio, swap_map, cluster_info, zeromap); spin_unlock(&si->lock); spin_unlock(&swap_lock); /* @@ -2684,7 +2695,7 @@ static void reinsert_swap_info(struct swap_info_struct *si) { spin_lock(&swap_lock); spin_lock(&si->lock); - setup_swap_info(si, si->prio, si->swap_map, si->cluster_info); + setup_swap_info(si, si->prio, si->swap_map, si->cluster_info, si->zeromap); _enable_swap_info(si); spin_unlock(&si->lock); spin_unlock(&swap_lock); @@ -2709,6 +2720,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) { struct swap_info_struct *p = NULL; unsigned char *swap_map; + unsigned long *zeromap; struct swap_cluster_info *cluster_info; struct file *swap_file, *victim; struct address_space *mapping; @@ -2831,6 +2843,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) p->max = 0; swap_map = p->swap_map; p->swap_map = NULL; + zeromap = p->zeromap; + p->zeromap = NULL; cluster_info = p->cluster_info; p->cluster_info = NULL; spin_unlock(&p->lock); @@ -2843,6 +2857,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) free_percpu(p->cluster_next_cpu); p->cluster_next_cpu = NULL; vfree(swap_map); + kvfree(zeromap); kvfree(cluster_info); /* Destroy swap account information */ swap_cgroup_swapoff(p->type); @@ -3340,6 +3355,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) sector_t span; unsigned long maxpages; unsigned char *swap_map = NULL; + unsigned long *zeromap = NULL; struct swap_cluster_info *cluster_info = NULL; struct page *page = NULL; struct inode *inode = NULL; @@ -3430,6 +3446,17 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) goto bad_swap_unlock_inode; } + /* + * Use kvmalloc_array instead of bitmap_zalloc as the allocation order might + * be above MAX_PAGE_ORDER incase of a large swap file. + */ + zeromap = kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long), + GFP_KERNEL | __GFP_ZERO); + if (!zeromap) { + error = -ENOMEM; + goto bad_swap_unlock_inode; + } + if (si->bdev && bdev_stable_writes(si->bdev)) si->flags |= SWP_STABLE_WRITES; @@ -3505,7 +3532,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) if (swap_flags & SWAP_FLAG_PREFER) prio = (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT; - enable_swap_info(si, prio, swap_map, cluster_info); + enable_swap_info(si, prio, swap_map, cluster_info, zeromap); pr_info("Adding %uk swap on %s. Priority:%d extents:%d across:%lluk %s%s%s%s\n", K(si->pages), name->name, si->prio, nr_extents, @@ -3540,6 +3567,7 @@ bad_swap: si->flags = 0; spin_unlock(&swap_lock); vfree(swap_map); + kvfree(zeromap); kvfree(cluster_info); if (inced_nr_rotate_swap) atomic_dec(&nr_rotate_swap);