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Message-ID: <CACePvbXpgZvESMm6RxZZ7b5=ju0neqxnFdjQXCCmDypfnp56DA@mail.gmail.com>
Date: Fri, 29 Aug 2025 19:31:44 -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 3/9] mm, swap: rename and move some swap cluster
definition and helpers
No functional change patch is easier to review :-)
Acked-by: Chris Li <chrisl@...nel.org>
Chris
On Fri, Aug 22, 2025 at 12:21 PM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> No feature change, move cluster related definitions and helpers to
> mm/swap.h, also tidy up and add a "swap_" prefix for cluster lock/unlock
> helpers, so they can be used outside of swap files.
>
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---
> include/linux/swap.h | 34 ---------------
> mm/swap.h | 63 ++++++++++++++++++++++++++++
> mm/swapfile.c | 99 ++++++++++++++------------------------------
> 3 files changed, 93 insertions(+), 103 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index c2da85cb7fe7..20efd9a34034 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -235,40 +235,6 @@ enum {
> /* Special value in each swap_map continuation */
> #define SWAP_CONT_MAX 0x7f /* Max count */
>
> -/*
> - * 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
> - * free clusters are organized into a list. We fetch an entry from the list to
> - * get a free cluster.
> - *
> - * The flags field determines if a cluster is free. This is
> - * protected by cluster lock.
> - */
> -struct swap_cluster_info {
> - spinlock_t lock; /*
> - * Protect swap_cluster_info fields
> - * other than list, and swap_info_struct->swap_map
> - * elements corresponding to the swap cluster.
> - */
> - u16 count;
> - u8 flags;
> - u8 order;
> - struct list_head list;
> -};
> -
> -/* All on-list cluster must have a non-zero flag. */
> -enum swap_cluster_flags {
> - CLUSTER_FLAG_NONE = 0, /* For temporary off-list cluster */
> - CLUSTER_FLAG_FREE,
> - CLUSTER_FLAG_NONFULL,
> - CLUSTER_FLAG_FRAG,
> - /* Clusters with flags above are allocatable */
> - CLUSTER_FLAG_USABLE = CLUSTER_FLAG_FRAG,
> - CLUSTER_FLAG_FULL,
> - CLUSTER_FLAG_DISCARD,
> - CLUSTER_FLAG_MAX,
> -};
> -
> /*
> * The first page in the swap file is the swap header, which is always marked
> * bad to prevent it from being allocated as an entry. This also prevents the
> diff --git a/mm/swap.h b/mm/swap.h
> index bb2adbfd64a9..223b40f2d37e 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -7,10 +7,73 @@ struct swap_iocb;
>
> extern int page_cluster;
>
> +#ifdef CONFIG_THP_SWAP
> +#define SWAPFILE_CLUSTER HPAGE_PMD_NR
> +#define swap_entry_order(order) (order)
> +#else
> +#define SWAPFILE_CLUSTER 256
> +#define swap_entry_order(order) 0
> +#endif
> +
> +/*
> + * 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
> + * free clusters are organized into a list. We fetch an entry from the list to
> + * get a free cluster.
> + *
> + * The flags field determines if a cluster is free. This is
> + * protected by cluster lock.
> + */
> +struct swap_cluster_info {
> + spinlock_t lock; /*
> + * Protect swap_cluster_info fields
> + * other than list, and swap_info_struct->swap_map
> + * elements corresponding to the swap cluster.
> + */
> + u16 count;
> + u8 flags;
> + u8 order;
> + struct list_head list;
> +};
> +
> +/* All on-list cluster must have a non-zero flag. */
> +enum swap_cluster_flags {
> + CLUSTER_FLAG_NONE = 0, /* For temporary off-list cluster */
> + CLUSTER_FLAG_FREE,
> + CLUSTER_FLAG_NONFULL,
> + CLUSTER_FLAG_FRAG,
> + /* Clusters with flags above are allocatable */
> + CLUSTER_FLAG_USABLE = CLUSTER_FLAG_FRAG,
> + CLUSTER_FLAG_FULL,
> + CLUSTER_FLAG_DISCARD,
> + CLUSTER_FLAG_MAX,
> +};
> +
> #ifdef CONFIG_SWAP
> #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(
> + struct swap_info_struct *si, pgoff_t offset)
> +{
> + return &si->cluster_info[offset / SWAPFILE_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);
> +
> + spin_lock(&ci->lock);
> + return ci;
> +}
> +
> +static inline void swap_cluster_unlock(struct swap_cluster_info *ci)
> +{
> + spin_unlock(&ci->lock);
> +}
> +
> /* linux/mm/page_io.c */
> int sio_pool_init(void);
> struct swap_iocb;
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 12f2580ebe8d..618cf4333a3d 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -58,9 +58,6 @@ static void swap_entries_free(struct swap_info_struct *si,
> static void swap_range_alloc(struct swap_info_struct *si,
> unsigned int nr_entries);
> static bool folio_swapcache_freeable(struct folio *folio);
> -static struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
> - unsigned long offset);
> -static inline void unlock_cluster(struct swap_cluster_info *ci);
>
> static DEFINE_SPINLOCK(swap_lock);
> static unsigned int nr_swapfiles;
> @@ -259,9 +256,9 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
> * swap_map is HAS_CACHE only, which means the slots have no page table
> * reference or pending writeback, and can't be allocated to others.
> */
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> need_reclaim = swap_only_has_cache(si, offset, nr_pages);
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> if (!need_reclaim)
> goto out_unlock;
>
> @@ -386,20 +383,7 @@ static void discard_swap_cluster(struct swap_info_struct *si,
> }
> }
>
> -#ifdef CONFIG_THP_SWAP
> -#define SWAPFILE_CLUSTER HPAGE_PMD_NR
> -
> -#define swap_entry_order(order) (order)
> -#else
> -#define SWAPFILE_CLUSTER 256
> -
> -/*
> - * Define swap_entry_order() as constant to let compiler to optimize
> - * out some code if !CONFIG_THP_SWAP
> - */
> -#define swap_entry_order(order) 0
> -#endif
> -#define LATENCY_LIMIT 256
> +#define LATENCY_LIMIT 256
>
> static inline bool cluster_is_empty(struct swap_cluster_info *info)
> {
> @@ -426,34 +410,12 @@ static inline unsigned int cluster_index(struct swap_info_struct *si,
> return ci - si->cluster_info;
> }
>
> -static inline struct swap_cluster_info *offset_to_cluster(struct swap_info_struct *si,
> - unsigned long offset)
> -{
> - return &si->cluster_info[offset / SWAPFILE_CLUSTER];
> -}
> -
> static inline unsigned int cluster_offset(struct swap_info_struct *si,
> struct swap_cluster_info *ci)
> {
> return cluster_index(si, ci) * SWAPFILE_CLUSTER;
> }
>
> -static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
> - unsigned long offset)
> -{
> - struct swap_cluster_info *ci;
> -
> - ci = offset_to_cluster(si, offset);
> - spin_lock(&ci->lock);
> -
> - return ci;
> -}
> -
> -static inline void unlock_cluster(struct swap_cluster_info *ci)
> -{
> - spin_unlock(&ci->lock);
> -}
> -
> static void move_cluster(struct swap_info_struct *si,
> struct swap_cluster_info *ci, struct list_head *list,
> enum swap_cluster_flags new_flags)
> @@ -809,7 +771,7 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
> }
> out:
> relocate_cluster(si, ci);
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> if (si->flags & SWP_SOLIDSTATE) {
> this_cpu_write(percpu_swap_cluster.offset[order], next);
> this_cpu_write(percpu_swap_cluster.si[order], si);
> @@ -876,7 +838,7 @@ static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
> if (ci->flags == CLUSTER_FLAG_NONE)
> relocate_cluster(si, ci);
>
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> if (to_scan <= 0)
> break;
> }
> @@ -915,7 +877,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> if (offset == SWAP_ENTRY_INVALID)
> goto new_cluster;
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> /* Cluster could have been used by another order */
> if (cluster_is_usable(ci, order)) {
> if (cluster_is_empty(ci))
> @@ -923,7 +885,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> found = alloc_swap_scan_cluster(si, ci, offset,
> order, usage);
> } else {
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> }
> if (found)
> goto done;
> @@ -1204,7 +1166,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
> if (!si || !offset || !get_swap_device_info(si))
> return false;
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> if (cluster_is_usable(ci, order)) {
> if (cluster_is_empty(ci))
> offset = cluster_offset(si, ci);
> @@ -1212,7 +1174,7 @@ static bool swap_alloc_fast(swp_entry_t *entry,
> if (found)
> *entry = swp_entry(si->type, found);
> } else {
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> }
>
> put_swap_device(si);
> @@ -1480,14 +1442,14 @@ static void swap_entries_put_cache(struct swap_info_struct *si,
> unsigned long offset = swp_offset(entry);
> struct swap_cluster_info *ci;
>
> - ci = lock_cluster(si, offset);
> - if (swap_only_has_cache(si, offset, nr))
> + ci = swap_cluster_lock(si, offset);
> + if (swap_only_has_cache(si, offset, nr)) {
> swap_entries_free(si, ci, entry, nr);
> - else {
> + } else {
> for (int i = 0; i < nr; i++, entry.val++)
> swap_entry_put_locked(si, ci, entry, SWAP_HAS_CACHE);
> }
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> }
>
> static bool swap_entries_put_map(struct swap_info_struct *si,
> @@ -1505,7 +1467,7 @@ static bool swap_entries_put_map(struct swap_info_struct *si,
> if (count != 1 && count != SWAP_MAP_SHMEM)
> goto fallback;
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> if (!swap_is_last_map(si, offset, nr, &has_cache)) {
> goto locked_fallback;
> }
> @@ -1514,21 +1476,20 @@ static bool swap_entries_put_map(struct swap_info_struct *si,
> else
> for (i = 0; i < nr; i++)
> WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
>
> return has_cache;
>
> fallback:
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> locked_fallback:
> for (i = 0; i < nr; i++, entry.val++) {
> count = swap_entry_put_locked(si, ci, entry, 1);
> if (count == SWAP_HAS_CACHE)
> has_cache = true;
> }
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> return has_cache;
> -
> }
>
> /*
> @@ -1578,7 +1539,7 @@ 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 != offset_to_cluster(si, offset + nr_pages - 1));
> + VM_BUG_ON(ci != swp_offset_cluster(si, offset + nr_pages - 1));
> VM_BUG_ON(cluster_is_empty(ci));
> VM_BUG_ON(ci->count < nr_pages);
>
> @@ -1653,9 +1614,9 @@ bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry)
> struct swap_cluster_info *ci;
> int count;
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> count = swap_count(si->swap_map[offset]);
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> return !!count;
> }
>
> @@ -1678,7 +1639,7 @@ int swp_swapcount(swp_entry_t entry)
>
> offset = swp_offset(entry);
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
>
> count = swap_count(si->swap_map[offset]);
> if (!(count & COUNT_CONTINUED))
> @@ -1701,7 +1662,7 @@ int swp_swapcount(swp_entry_t entry)
> n *= (SWAP_CONT_MAX + 1);
> } while (tmp_count & COUNT_CONTINUED);
> out:
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> return count;
> }
>
> @@ -1716,7 +1677,7 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
> int i;
> bool ret = false;
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
> if (nr_pages == 1) {
> if (swap_count(map[roffset]))
> ret = true;
> @@ -1729,7 +1690,7 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
> }
> }
> unlock_out:
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> return ret;
> }
>
> @@ -2662,8 +2623,8 @@ static void wait_for_allocation(struct swap_info_struct *si)
> BUG_ON(si->flags & SWP_WRITEOK);
>
> for (offset = 0; offset < end; offset += SWAPFILE_CLUSTER) {
> - ci = lock_cluster(si, offset);
> - unlock_cluster(ci);
> + ci = swap_cluster_lock(si, offset);
> + swap_cluster_unlock(ci);
> }
> }
>
> @@ -3579,7 +3540,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
> offset = swp_offset(entry);
> VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
> VM_WARN_ON(usage == 1 && nr > 1);
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
>
> err = 0;
> for (i = 0; i < nr; i++) {
> @@ -3634,7 +3595,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
> }
>
> unlock_out:
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> return err;
> }
>
> @@ -3733,7 +3694,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
>
> offset = swp_offset(entry);
>
> - ci = lock_cluster(si, offset);
> + ci = swap_cluster_lock(si, offset);
>
> count = swap_count(si->swap_map[offset]);
>
> @@ -3793,7 +3754,7 @@ int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
> out_unlock_cont:
> spin_unlock(&si->cont_lock);
> out:
> - unlock_cluster(ci);
> + swap_cluster_unlock(ci);
> put_swap_device(si);
> outer:
> if (page)
> --
> 2.51.0
>
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