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Message-ID: <18a6bed3-112b-4107-9aaa-6963b6b0bc08@linux.alibaba.com>
Date: Tue, 30 Jul 2024 16:15:18 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
linux-mm@...ck.org
Cc: chrisl@...nel.org, david@...hat.com, hannes@...xchg.org,
hughd@...gle.com, kaleshsingh@...gle.com, kasong@...cent.com,
linux-kernel@...r.kernel.org, mhocko@...e.com, minchan@...nel.org,
nphamcs@...il.com, ryan.roberts@....com, senozhatsky@...omium.org,
shakeel.butt@...ux.dev, shy828301@...il.com, surenb@...gle.com,
v-songbaohua@...o.com, willy@...radead.org, xiang@...nel.org,
ying.huang@...el.com, yosryahmed@...gle.com
Subject: Re: [PATCH 1/1] mm: swap: add nr argument in swapcache_prepare and
swapcache_clear to support large folios
On 2024/7/30 15:13, Barry Song wrote:
> From: Barry Song <v-songbaohua@...o.com>
>
> Right now, swapcache_prepare() and swapcache_clear() supports one entry
> only, to support large folios, we need to handle multiple swap entries.
>
> To optimize stack usage, we iterate twice in __swap_duplicate(): the
> first time to verify that all entries are valid, and the second time
> to apply the modifications to the entries.
>
> Currently, we're using nr=1 for the existing users.
>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
Thanks Barry. Tested it with my shmem swap patches, and works well. So
Tested-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> include/linux/swap.h | 4 +-
> mm/memory.c | 6 +--
> mm/swap.h | 5 ++-
> mm/swap_state.c | 2 +-
> mm/swapfile.c | 101 +++++++++++++++++++++++++------------------
> 5 files changed, 68 insertions(+), 50 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index ba7ea95d1c57..5b920fa2315b 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -480,7 +480,7 @@ extern int get_swap_pages(int n, swp_entry_t swp_entries[], int order);
> extern int add_swap_count_continuation(swp_entry_t, gfp_t);
> extern void swap_shmem_alloc(swp_entry_t);
> extern int swap_duplicate(swp_entry_t);
> -extern int swapcache_prepare(swp_entry_t);
> +extern int swapcache_prepare(swp_entry_t entry, int nr);
> extern void swap_free_nr(swp_entry_t entry, int nr_pages);
> extern void swapcache_free_entries(swp_entry_t *entries, int n);
> extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
> @@ -554,7 +554,7 @@ static inline int swap_duplicate(swp_entry_t swp)
> return 0;
> }
>
> -static inline int swapcache_prepare(swp_entry_t swp)
> +static inline int swapcache_prepare(swp_entry_t swp, int nr)
> {
> return 0;
> }
> diff --git a/mm/memory.c b/mm/memory.c
> index 833d2cad6eb2..b8675617a5e3 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4081,7 +4081,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> * reusing the same entry. It's undetectable as
> * pte_same() returns true due to entry reuse.
> */
> - if (swapcache_prepare(entry)) {
> + if (swapcache_prepare(entry, 1)) {
> /* Relax a bit to prevent rapid repeated page faults */
> schedule_timeout_uninterruptible(1);
> goto out;
> @@ -4387,7 +4387,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> out:
> /* Clear the swap cache pin for direct swapin after PTL unlock */
> if (need_clear_cache)
> - swapcache_clear(si, entry);
> + swapcache_clear(si, entry, 1);
> if (si)
> put_swap_device(si);
> return ret;
> @@ -4403,7 +4403,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> folio_put(swapcache);
> }
> if (need_clear_cache)
> - swapcache_clear(si, entry);
> + swapcache_clear(si, entry, 1);
> if (si)
> put_swap_device(si);
> return ret;
> diff --git a/mm/swap.h b/mm/swap.h
> index baa1fa946b34..7c6330561d84 100644
> --- a/mm/swap.h
> +++ b/mm/swap.h
> @@ -59,7 +59,7 @@ void __delete_from_swap_cache(struct folio *folio,
> void delete_from_swap_cache(struct folio *folio);
> void clear_shadow_from_swap_cache(int type, unsigned long begin,
> unsigned long end);
> -void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry);
> +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr);
> struct folio *swap_cache_get_folio(swp_entry_t entry,
> struct vm_area_struct *vma, unsigned long addr);
> struct folio *filemap_get_incore_folio(struct address_space *mapping,
> @@ -120,7 +120,7 @@ static inline int swap_writepage(struct page *p, struct writeback_control *wbc)
> return 0;
> }
>
> -static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
> +static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr)
> {
> }
>
> @@ -172,4 +172,5 @@ static inline unsigned int folio_swap_flags(struct folio *folio)
> return 0;
> }
> #endif /* CONFIG_SWAP */
> +
> #endif /* _MM_SWAP_H */
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index a1726e49a5eb..b06f2a054f5a 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -477,7 +477,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
> /*
> * Swap entry may have been freed since our caller observed it.
> */
> - err = swapcache_prepare(entry);
> + err = swapcache_prepare(entry, 1);
> if (!err)
> break;
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 5f73a8553371..757d38a86f56 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3363,7 +3363,7 @@ void si_swapinfo(struct sysinfo *val)
> }
>
> /*
> - * Verify that a swap entry is valid and increment its swap map count.
> + * Verify that nr swap entries are valid and increment their swap map counts.
> *
> * Returns error code in following case.
> * - success -> 0
> @@ -3373,60 +3373,77 @@ void si_swapinfo(struct sysinfo *val)
> * - swap-cache reference is requested but the entry is not used. -> ENOENT
> * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
> */
> -static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
> +static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
> {
> struct swap_info_struct *p;
> struct swap_cluster_info *ci;
> unsigned long offset;
> unsigned char count;
> unsigned char has_cache;
> - int err;
> + int err, i;
>
> p = swp_swap_info(entry);
>
> offset = swp_offset(entry);
> + VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
> ci = lock_cluster_or_swap_info(p, offset);
>
> - count = p->swap_map[offset];
> + err = 0;
> + for (i = 0; i < nr; i++) {
> + count = p->swap_map[offset + i];
>
> - /*
> - * swapin_readahead() doesn't check if a swap entry is valid, so the
> - * swap entry could be SWAP_MAP_BAD. Check here with lock held.
> - */
> - if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
> - err = -ENOENT;
> - goto unlock_out;
> - }
> + /*
> + * swapin_readahead() doesn't check if a swap entry is valid, so the
> + * swap entry could be SWAP_MAP_BAD. Check here with lock held.
> + */
> + if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
> + err = -ENOENT;
> + goto unlock_out;
> + }
>
> - has_cache = count & SWAP_HAS_CACHE;
> - count &= ~SWAP_HAS_CACHE;
> - err = 0;
> + has_cache = count & SWAP_HAS_CACHE;
> + count &= ~SWAP_HAS_CACHE;
>
> - if (usage == SWAP_HAS_CACHE) {
> + if (usage == SWAP_HAS_CACHE) {
> + /* set SWAP_HAS_CACHE if there is no cache and entry is used */
> + if (!has_cache && count)
> + continue;
> + else if (has_cache) /* someone else added cache */
> + err = -EEXIST;
> + else /* no users remaining */
> + err = -ENOENT;
>
> - /* set SWAP_HAS_CACHE if there is no cache and entry is used */
> - if (!has_cache && count)
> - has_cache = SWAP_HAS_CACHE;
> - else if (has_cache) /* someone else added cache */
> - err = -EEXIST;
> - else /* no users remaining */
> - err = -ENOENT;
> + } else if (count || has_cache) {
>
> - } else if (count || has_cache) {
> + if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
> + continue;
> + else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
> + err = -EINVAL;
> + else if (swap_count_continued(p, offset + i, count))
> + continue;
> + else
> + err = -ENOMEM;
> + } else
> + err = -ENOENT; /* unused swap entry */
>
> - if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
> + if (err)
> + goto unlock_out;
> + }
> +
> + for (i = 0; i < nr; i++) {
> + count = p->swap_map[offset + i];
> + has_cache = count & SWAP_HAS_CACHE;
> + count &= ~SWAP_HAS_CACHE;
> +
> + if (usage == SWAP_HAS_CACHE)
> + has_cache = SWAP_HAS_CACHE;
> + else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
> count += usage;
> - else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
> - err = -EINVAL;
> - else if (swap_count_continued(p, offset, count))
> - count = COUNT_CONTINUED;
> else
> - err = -ENOMEM;
> - } else
> - err = -ENOENT; /* unused swap entry */
> + count = COUNT_CONTINUED;
>
> - if (!err)
> - WRITE_ONCE(p->swap_map[offset], count | has_cache);
> + WRITE_ONCE(p->swap_map[offset + i], count | has_cache);
> + }
>
> unlock_out:
> unlock_cluster_or_swap_info(p, ci);
> @@ -3439,7 +3456,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
> */
> void swap_shmem_alloc(swp_entry_t entry)
> {
> - __swap_duplicate(entry, SWAP_MAP_SHMEM);
> + __swap_duplicate(entry, SWAP_MAP_SHMEM, 1);
> }
>
> /*
> @@ -3453,29 +3470,29 @@ int swap_duplicate(swp_entry_t entry)
> {
> int err = 0;
>
> - while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
> + while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM)
> err = add_swap_count_continuation(entry, GFP_ATOMIC);
> return err;
> }
>
> /*
> - * @entry: swap entry for which we allocate swap cache.
> + * @entry: first swap entry from which we allocate nr swap cache.
> *
> - * Called when allocating swap cache for existing swap entry,
> + * Called when allocating swap cache for existing swap entries,
> * This can return error codes. Returns 0 at success.
> * -EEXIST means there is a swap cache.
> * Note: return code is different from swap_duplicate().
> */
> -int swapcache_prepare(swp_entry_t entry)
> +int swapcache_prepare(swp_entry_t entry, int nr)
> {
> - return __swap_duplicate(entry, SWAP_HAS_CACHE);
> + return __swap_duplicate(entry, SWAP_HAS_CACHE, nr);
> }
>
> -void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
> +void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr)
> {
> unsigned long offset = swp_offset(entry);
>
> - cluster_swap_free_nr(si, offset, 1, SWAP_HAS_CACHE);
> + cluster_swap_free_nr(si, offset, nr, SWAP_HAS_CACHE);
> }
>
> struct swap_info_struct *swp_swap_info(swp_entry_t entry)
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