[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAF8kJuMKRbxd=4vNaCwOmKWRQtBRsGczzeoFa6tAj0HL1To0sg@mail.gmail.com>
Date: Fri, 5 Sep 2025 19:14:19 -0700
From: Chris Li <chrisl@...nel.org>
To: Kairui Song <kasong@...cent.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>, Barry Song <baohua@...nel.org>,
Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>,
Kemeng Shi <shikemeng@...weicloud.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
Ying Huang <ying.huang@...ux.alibaba.com>, Johannes Weiner <hannes@...xchg.org>,
David Hildenbrand <david@...hat.com>, Yosry Ahmed <yosryahmed@...gle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 07/15] mm, swap: tidy up swap device and cluster info helpers
Acked-by: Chris Li <chrisl@...nel.org>
Chris
On Fri, Sep 5, 2025 at 12:14 PM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> swp_swap_info is the most commonly used helper for retrieving swap info.
> It has an internal check that may lead to a NULL return value, but
> almost none of its caller checks the return value, making the internal
> check pointless. In fact, most of these callers already ensured the
> entry is valid and never expect a NULL value.
>
> Tidy this up and shorten the name. If the caller can make sure the
> swap entry/type is valid and the device is pinned, use the new introduced
> __swap_entry_to_info/__swap_type_to_info instead. They have more debug
> sanity checks and lower overhead as they are inlined.
>
> Callers that may expect a NULL value should use
> swap_entry_to_info/swap_type_to_info instead.
>
> No feature change. The rearranged codes should have had no effect, or
> they should have been hitting NULL de-ref bugs already. Only some new
> sanity checks are added so potential issues may show up in debug build.
>
> The new helpers will be frequently used with swap table later when working
> with swap cache folios. A locked swap cache folio ensures the entries are
> valid and stable so these helpers are very helpful.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> Acked-by: Chris Li <chrisl@...nel.org>
> Reviewed-by: Barry Song <baohua@...nel.org>
> ---
> include/linux/swap.h | 6 ------
> mm/page_io.c | 12 ++++++------
> mm/swap.h | 38 +++++++++++++++++++++++++++++++++-----
> mm/swap_state.c | 4 ++--
> mm/swapfile.c | 37 +++++++++++++++++++------------------
> 5 files changed, 60 insertions(+), 37 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 7e1fe4ff3d30..6db105383782 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -479,7 +479,6 @@ extern sector_t swapdev_block(int, pgoff_t);
> 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);
> -struct swap_info_struct *swp_swap_info(swp_entry_t entry);
> struct backing_dev_info;
> extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
> extern void exit_swap_address_space(unsigned int type);
> @@ -492,11 +491,6 @@ static inline void put_swap_device(struct swap_info_struct *si)
> }
>
> #else /* CONFIG_SWAP */
> -static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry)
> -{
> - return NULL;
> -}
> -
> static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)
> {
> return NULL;
> diff --git a/mm/page_io.c b/mm/page_io.c
> index a2056a5ecb13..3c342db77ce3 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -204,7 +204,7 @@ static bool is_folio_zero_filled(struct folio *folio)
> static void swap_zeromap_folio_set(struct folio *folio)
> {
> struct obj_cgroup *objcg = get_obj_cgroup_from_folio(folio);
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> int nr_pages = folio_nr_pages(folio);
> swp_entry_t entry;
> unsigned int i;
> @@ -223,7 +223,7 @@ static void swap_zeromap_folio_set(struct folio *folio)
>
> static void swap_zeromap_folio_clear(struct folio *folio)
> {
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> swp_entry_t entry;
> unsigned int i;
>
> @@ -374,7 +374,7 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
> static void swap_writepage_fs(struct folio *folio, struct swap_iocb **swap_plug)
> {
> struct swap_iocb *sio = swap_plug ? *swap_plug : NULL;
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + 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);
>
> @@ -446,7 +446,7 @@ static void swap_writepage_bdev_async(struct folio *folio,
>
> void __swap_writepage(struct folio *folio, struct swap_iocb **swap_plug)
> {
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
>
> VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
> /*
> @@ -537,7 +537,7 @@ static bool swap_read_folio_zeromap(struct folio *folio)
>
> static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
> {
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> struct swap_iocb *sio = NULL;
> loff_t pos = swap_dev_pos(folio->swap);
>
> @@ -608,7 +608,7 @@ static void swap_read_folio_bdev_async(struct folio *folio,
>
> void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
> {
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
> bool workingset = folio_test_workingset(folio);
> unsigned long pflags;
> diff --git a/mm/swap.h b/mm/swap.h
> index 39b27337bc0a..a65e72edb087 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -15,6 +15,8 @@ extern int page_cluster;
> #define swap_entry_order(order) 0
> #endif
>
> +extern struct swap_info_struct *swap_info[];
> +
> /*
> * We use this to track usage of a cluster. A cluster is a block of swap disk
> * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
> @@ -53,9 +55,29 @@ enum swap_cluster_flags {
> #include <linux/swapops.h> /* for swp_offset */
> #include <linux/blk_types.h> /* for bio_end_io_t */
>
> -static inline struct swap_cluster_info *swp_offset_cluster(
> +/*
> + * Callers of all helpers below must ensure the entry, type, or offset is
> + * valid, and protect the swap device with reference count or locks.
> + */
> +static inline struct swap_info_struct *__swap_type_to_info(int type)
> +{
> + struct swap_info_struct *si;
> +
> + si = READ_ONCE(swap_info[type]); /* rcu_dereference() */
> + VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
> + return si;
> +}
> +
> +static inline struct swap_info_struct *__swap_entry_to_info(swp_entry_t entry)
> +{
> + return __swap_type_to_info(swp_type(entry));
> +}
> +
> +static inline struct swap_cluster_info *__swap_offset_to_cluster(
> struct swap_info_struct *si, pgoff_t offset)
> {
> + VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
> + VM_WARN_ON_ONCE(offset >= si->max);
> return &si->cluster_info[offset / SWAPFILE_CLUSTER];
> }
>
> @@ -70,8 +92,9 @@ static inline struct swap_cluster_info *swp_offset_cluster(
> static inline struct swap_cluster_info *swap_cluster_lock(
> struct swap_info_struct *si, unsigned long offset)
> {
> - struct swap_cluster_info *ci = swp_offset_cluster(si, offset);
> + struct swap_cluster_info *ci = __swap_offset_to_cluster(si, offset);
>
> + VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
> spin_lock(&ci->lock);
> return ci;
> }
> @@ -167,7 +190,7 @@ void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma,
>
> static inline unsigned int folio_swap_flags(struct folio *folio)
> {
> - return swp_swap_info(folio->swap)->flags;
> + return __swap_entry_to_info(folio->swap)->flags;
> }
>
> /*
> @@ -178,7 +201,7 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
> static inline int swap_zeromap_batch(swp_entry_t entry, int max_nr,
> bool *is_zeromap)
> {
> - struct swap_info_struct *sis = swp_swap_info(entry);
> + struct swap_info_struct *sis = __swap_entry_to_info(entry);
> unsigned long start = swp_offset(entry);
> unsigned long end = start + max_nr;
> bool first_bit;
> @@ -197,7 +220,7 @@ static inline int swap_zeromap_batch(swp_entry_t entry, int max_nr,
>
> static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
> {
> - struct swap_info_struct *si = swp_swap_info(entry);
> + struct swap_info_struct *si = __swap_entry_to_info(entry);
> pgoff_t offset = swp_offset(entry);
> int i;
>
> @@ -216,6 +239,11 @@ static inline int non_swapcache_batch(swp_entry_t entry, int max_nr)
>
> #else /* CONFIG_SWAP */
> struct swap_iocb;
> +static inline struct swap_info_struct *__swap_entry_to_info(swp_entry_t entry)
> +{
> + return NULL;
> +}
> +
> static inline void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
> {
> }
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 9225d6b695ad..0ad4f3b41f1b 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -336,7 +336,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> struct mempolicy *mpol, pgoff_t ilx, bool *new_page_allocated,
> bool skip_if_exists)
> {
> - struct swap_info_struct *si = swp_swap_info(entry);
> + struct swap_info_struct *si = __swap_entry_to_info(entry);
> struct folio *folio;
> struct folio *new_folio = NULL;
> struct folio *result = NULL;
> @@ -560,7 +560,7 @@ struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
> unsigned long offset = entry_offset;
> unsigned long start_offset, end_offset;
> unsigned long mask;
> - struct swap_info_struct *si = swp_swap_info(entry);
> + struct swap_info_struct *si = __swap_entry_to_info(entry);
> struct blk_plug plug;
> struct swap_iocb *splug = NULL;
> bool page_allocated;
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 547ad4bfe1d8..367481d319cd 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -102,7 +102,7 @@ static PLIST_HEAD(swap_active_head);
> static struct plist_head *swap_avail_heads;
> static DEFINE_SPINLOCK(swap_avail_lock);
>
> -static struct swap_info_struct *swap_info[MAX_SWAPFILES];
> +struct swap_info_struct *swap_info[MAX_SWAPFILES];
>
> static DEFINE_MUTEX(swapon_mutex);
>
> @@ -124,14 +124,20 @@ static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = {
> .lock = INIT_LOCAL_LOCK(),
> };
>
> -static struct swap_info_struct *swap_type_to_swap_info(int type)
> +/* May return NULL on invalid type, caller must check for NULL return */
> +static struct swap_info_struct *swap_type_to_info(int type)
> {
> if (type >= MAX_SWAPFILES)
> return NULL;
> -
> return READ_ONCE(swap_info[type]); /* rcu_dereference() */
> }
>
> +/* May return NULL on invalid entry, caller must check for NULL return */
> +static struct swap_info_struct *swap_entry_to_info(swp_entry_t entry)
> +{
> + return swap_type_to_info(swp_type(entry));
> +}
> +
> static inline unsigned char swap_count(unsigned char ent)
> {
> return ent & ~SWAP_HAS_CACHE; /* may include COUNT_CONTINUED flag */
> @@ -341,7 +347,7 @@ offset_to_swap_extent(struct swap_info_struct *sis, unsigned long offset)
>
> sector_t swap_folio_sector(struct folio *folio)
> {
> - struct swap_info_struct *sis = swp_swap_info(folio->swap);
> + struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
> struct swap_extent *se;
> sector_t sector;
> pgoff_t offset;
> @@ -1299,7 +1305,7 @@ static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
>
> if (!entry.val)
> goto out;
> - si = swp_swap_info(entry);
> + si = swap_entry_to_info(entry);
> if (!si)
> goto bad_nofile;
> if (data_race(!(si->flags & SWP_USED)))
> @@ -1414,7 +1420,7 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
>
> if (!entry.val)
> goto out;
> - si = swp_swap_info(entry);
> + si = swap_entry_to_info(entry);
> if (!si)
> goto bad_nofile;
> if (!get_swap_device_info(si))
> @@ -1537,7 +1543,7 @@ static void swap_entries_free(struct swap_info_struct *si,
> unsigned char *map_end = map + nr_pages;
>
> /* It should never free entries across different clusters */
> - VM_BUG_ON(ci != swp_offset_cluster(si, offset + nr_pages - 1));
> + VM_BUG_ON(ci != __swap_offset_to_cluster(si, offset + nr_pages - 1));
> VM_BUG_ON(cluster_is_empty(ci));
> VM_BUG_ON(ci->count < nr_pages);
>
> @@ -1595,7 +1601,7 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
>
> int __swap_count(swp_entry_t entry)
> {
> - struct swap_info_struct *si = swp_swap_info(entry);
> + struct swap_info_struct *si = __swap_entry_to_info(entry);
> pgoff_t offset = swp_offset(entry);
>
> return swap_count(si->swap_map[offset]);
> @@ -1826,7 +1832,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
>
> swp_entry_t get_swap_page_of_type(int type)
> {
> - struct swap_info_struct *si = swap_type_to_swap_info(type);
> + struct swap_info_struct *si = swap_type_to_info(type);
> unsigned long offset;
> swp_entry_t entry = {0};
>
> @@ -1907,7 +1913,7 @@ int find_first_swap(dev_t *device)
> */
> sector_t swapdev_block(int type, pgoff_t offset)
> {
> - struct swap_info_struct *si = swap_type_to_swap_info(type);
> + struct swap_info_struct *si = swap_type_to_info(type);
> struct swap_extent *se;
>
> if (!si || !(si->flags & SWP_WRITEOK))
> @@ -2835,7 +2841,7 @@ static void *swap_start(struct seq_file *swap, loff_t *pos)
> if (!l)
> return SEQ_START_TOKEN;
>
> - for (type = 0; (si = swap_type_to_swap_info(type)); type++) {
> + for (type = 0; (si = swap_type_to_info(type)); type++) {
> if (!(si->flags & SWP_USED) || !si->swap_map)
> continue;
> if (!--l)
> @@ -2856,7 +2862,7 @@ static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
> type = si->type + 1;
>
> ++(*pos);
> - for (; (si = swap_type_to_swap_info(type)); type++) {
> + for (; (si = swap_type_to_info(type)); type++) {
> if (!(si->flags & SWP_USED) || !si->swap_map)
> continue;
> return si;
> @@ -3529,7 +3535,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
> unsigned char has_cache;
> int err, i;
>
> - si = swp_swap_info(entry);
> + si = swap_entry_to_info(entry);
> if (WARN_ON_ONCE(!si)) {
> pr_err("%s%08lx\n", Bad_file, entry.val);
> return -EINVAL;
> @@ -3644,11 +3650,6 @@ void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr)
> swap_entries_put_cache(si, entry, nr);
> }
>
> -struct swap_info_struct *swp_swap_info(swp_entry_t entry)
> -{
> - return swap_type_to_swap_info(swp_type(entry));
> -}
> -
> /*
> * add_swap_count_continuation - called when a swap count is duplicated
> * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
> --
> 2.51.0
>
>
Powered by blists - more mailing lists