| Message ID | 20240311150058.1122862-3-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Swap-out mTHP without splitting | expand |
Hi David, I hate to chase, but since you provided feedback on a couple of the other patches in the series, I wondered if you missed this one? It's the one that does the batching of free_swap_and_cache(), which you suggested in order to prevent needlessly taking folio locks and refs. If you have any feedback, it would be appreciated, otherwise I'm planning to repost as-is next week (nobody else has posted comments against this patch either) as part of the updated series. Thanks, Ryan On 11/03/2024 15:00, Ryan Roberts wrote: > Now that we no longer have a convenient flag in the cluster to determine > if a folio is large, free_swap_and_cache() will take a reference and > lock a large folio much more often, which could lead to contention and > (e.g.) failure to split large folios, etc. > > Let's solve that problem by batch freeing swap and cache with a new > function, free_swap_and_cache_nr(), to free a contiguous range of swap > entries together. This allows us to first drop a reference to each swap > slot before we try to release the cache folio. This means we only try to > release the folio once, only taking the reference and lock once - much > better than the previous 512 times for the 2M THP case. > > Contiguous swap entries are gathered in zap_pte_range() and > madvise_free_pte_range() in a similar way to how present ptes are > already gathered in zap_pte_range(). > > While we are at it, let's simplify by converting the return type of both > functions to void. The return value was used only by zap_pte_range() to > print a bad pte, and was ignored by everyone else, so the extra > reporting wasn't exactly guaranteed. We will still get the warning with > most of the information from get_swap_device(). With the batch version, > we wouldn't know which pte was bad anyway so could print the wrong one. > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > --- > include/linux/pgtable.h | 28 +++++++++++++++ > include/linux/swap.h | 12 +++++-- > mm/internal.h | 48 +++++++++++++++++++++++++ > mm/madvise.c | 12 ++++--- > mm/memory.c | 13 +++---- > mm/swapfile.c | 78 ++++++++++++++++++++++++++++++----------- > 6 files changed, 157 insertions(+), 34 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 85fc7554cd52..8cf1f2fe2c25 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -708,6 +708,34 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm, > } > #endif > > +#ifndef clear_not_present_full_ptes > +/** > + * clear_not_present_full_ptes - Clear consecutive not present PTEs. > + * @mm: Address space the ptes represent. > + * @addr: Address of the first pte. > + * @ptep: Page table pointer for the first entry. > + * @nr: Number of entries to clear. > + * @full: Whether we are clearing a full mm. > + * > + * May be overridden by the architecture; otherwise, implemented as a simple > + * loop over pte_clear_not_present_full(). > + * > + * Context: The caller holds the page table lock. The PTEs are all not present. > + * The PTEs are all in the same PMD. > + */ > +static inline void clear_not_present_full_ptes(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, unsigned int nr, int full) > +{ > + for (;;) { > + pte_clear_not_present_full(mm, addr, ptep, full); > + if (--nr == 0) > + break; > + ptep++; > + addr += PAGE_SIZE; > + } > +} > +#endif > + > #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH > extern pte_t ptep_clear_flush(struct vm_area_struct *vma, > unsigned long address, > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 4a8b6c60793a..f2b7f204b968 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -481,7 +481,7 @@ extern int swap_duplicate(swp_entry_t); > extern int swapcache_prepare(swp_entry_t); > extern void swap_free(swp_entry_t); > extern void swapcache_free_entries(swp_entry_t *entries, int n); > -extern int free_swap_and_cache(swp_entry_t); > +extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); > int swap_type_of(dev_t device, sector_t offset); > int find_first_swap(dev_t *device); > extern unsigned int count_swap_pages(int, int); > @@ -530,8 +530,9 @@ static inline void put_swap_device(struct swap_info_struct *si) > #define free_pages_and_swap_cache(pages, nr) \ > release_pages((pages), (nr)); > > -/* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */ > -#define free_swap_and_cache(e) is_pfn_swap_entry(e) > +static inline void free_swap_and_cache_nr(swp_entry_t entry, int nr) > +{ > +} > > static inline void free_swap_cache(struct folio *folio) > { > @@ -599,6 +600,11 @@ static inline int add_swap_extent(struct swap_info_struct *sis, > } > #endif /* CONFIG_SWAP */ > > +static inline void free_swap_and_cache(swp_entry_t entry) > +{ > + free_swap_and_cache_nr(entry, 1); > +} > + > #ifdef CONFIG_MEMCG > static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) > { > diff --git a/mm/internal.h b/mm/internal.h > index a3e19194079f..8dbb1335df88 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -11,6 +11,8 @@ > #include <linux/mm.h> > #include <linux/pagemap.h> > #include <linux/rmap.h> > +#include <linux/swap.h> > +#include <linux/swapops.h> > #include <linux/tracepoint-defs.h> > > struct folio_batch; > @@ -174,6 +176,52 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > > return min(ptep - start_ptep, max_nr); > } > + > +/** > + * swap_pte_batch - detect a PTE batch for a set of contiguous swap entries > + * @start_ptep: Page table pointer for the first entry. > + * @max_nr: The maximum number of table entries to consider. > + * @entry: Swap entry recovered from the first table entry. > + * > + * Detect a batch of contiguous swap entries: consecutive (non-present) PTEs > + * containing swap entries all with consecutive offsets and targeting the same > + * swap type. > + * > + * max_nr must be at least one and must be limited by the caller so scanning > + * cannot exceed a single page table. > + * > + * Return: the number of table entries in the batch. > + */ > +static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, > + swp_entry_t entry) > +{ > + const pte_t *end_ptep = start_ptep + max_nr; > + unsigned long expected_offset = swp_offset(entry) + 1; > + unsigned int expected_type = swp_type(entry); > + pte_t *ptep = start_ptep + 1; > + > + VM_WARN_ON(max_nr < 1); > + VM_WARN_ON(non_swap_entry(entry)); > + > + while (ptep < end_ptep) { > + pte_t pte = ptep_get(ptep); > + > + if (pte_none(pte) || pte_present(pte)) > + break; > + > + entry = pte_to_swp_entry(pte); > + > + if (non_swap_entry(entry) || > + swp_type(entry) != expected_type || > + swp_offset(entry) != expected_offset) > + break; > + > + expected_offset++; > + ptep++; > + } > + > + return ptep - start_ptep; > +} > #endif /* CONFIG_MMU */ > > void __acct_reclaim_writeback(pg_data_t *pgdat, struct folio *folio, > diff --git a/mm/madvise.c b/mm/madvise.c > index 44a498c94158..547dcd1f7a39 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -628,6 +628,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > struct folio *folio; > int nr_swap = 0; > unsigned long next; > + int nr, max_nr; > > next = pmd_addr_end(addr, end); > if (pmd_trans_huge(*pmd)) > @@ -640,7 +641,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > return 0; > flush_tlb_batched_pending(mm); > arch_enter_lazy_mmu_mode(); > - for (; addr != end; pte++, addr += PAGE_SIZE) { > + for (; addr != end; pte += nr, addr += PAGE_SIZE * nr) { > + nr = 1; > ptent = ptep_get(pte); > > if (pte_none(ptent)) > @@ -655,9 +657,11 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, > > entry = pte_to_swp_entry(ptent); > if (!non_swap_entry(entry)) { > - nr_swap--; > - free_swap_and_cache(entry); > - pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); > + max_nr = (end - addr) / PAGE_SIZE; > + nr = swap_pte_batch(pte, max_nr, entry); > + nr_swap -= nr; > + free_swap_and_cache_nr(entry, nr); > + clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm); > } else if (is_hwpoison_entry(entry) || > is_poisoned_swp_entry(entry)) { > pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); > diff --git a/mm/memory.c b/mm/memory.c > index f2bc6dd15eb8..25c0ef1c7ff3 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1629,12 +1629,13 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, > folio_remove_rmap_pte(folio, page, vma); > folio_put(folio); > } else if (!non_swap_entry(entry)) { > - /* Genuine swap entry, hence a private anon page */ > + max_nr = (end - addr) / PAGE_SIZE; > + nr = swap_pte_batch(pte, max_nr, entry); > + /* Genuine swap entries, hence a private anon pages */ > if (!should_zap_cows(details)) > continue; > - rss[MM_SWAPENTS]--; > - if (unlikely(!free_swap_and_cache(entry))) > - print_bad_pte(vma, addr, ptent, NULL); > + rss[MM_SWAPENTS] -= nr; > + free_swap_and_cache_nr(entry, nr); > } else if (is_migration_entry(entry)) { > folio = pfn_swap_entry_folio(entry); > if (!should_zap_folio(details, folio)) > @@ -1657,8 +1658,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, > pr_alert("unrecognized swap entry 0x%lx\n", entry.val); > WARN_ON_ONCE(1); > } > - pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); > - zap_install_uffd_wp_if_needed(vma, addr, pte, 1, details, ptent); > + clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm); > + zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details, ptent); > } while (pte += nr, addr += PAGE_SIZE * nr, addr != end); > > add_mm_rss_vec(mm, rss); > diff --git a/mm/swapfile.c b/mm/swapfile.c > index df1de034f6d8..ee7e44cb40c5 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -130,7 +130,11 @@ static inline unsigned char swap_count(unsigned char ent) > /* Reclaim the swap entry if swap is getting full*/ > #define TTRS_FULL 0x4 > > -/* returns 1 if swap entry is freed */ > +/* > + * returns number of pages in the folio that backs the swap entry. If positive, > + * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no > + * folio was associated with the swap entry. > + */ > static int __try_to_reclaim_swap(struct swap_info_struct *si, > unsigned long offset, unsigned long flags) > { > @@ -155,6 +159,7 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si, > ret = folio_free_swap(folio); > folio_unlock(folio); > } > + ret = ret ? folio_nr_pages(folio) : -folio_nr_pages(folio); > folio_put(folio); > return ret; > } > @@ -895,7 +900,7 @@ static int scan_swap_map_slots(struct swap_info_struct *si, > swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY); > spin_lock(&si->lock); > /* entry was freed successfully, try to use this again */ > - if (swap_was_freed) > + if (swap_was_freed > 0) > goto checks; > goto scan; /* check next one */ > } > @@ -1572,32 +1577,63 @@ bool folio_free_swap(struct folio *folio) > return true; > } > > -/* > - * Free the swap entry like above, but also try to > - * free the page cache entry if it is the last user. > - */ > -int free_swap_and_cache(swp_entry_t entry) > +void free_swap_and_cache_nr(swp_entry_t entry, int nr) > { > - struct swap_info_struct *p; > - unsigned char count; > + unsigned long end = swp_offset(entry) + nr; > + unsigned int type = swp_type(entry); > + struct swap_info_struct *si; > + unsigned long offset; > > if (non_swap_entry(entry)) > - return 1; > + return; > > - p = get_swap_device(entry); > - if (p) { > - if (WARN_ON(data_race(!p->swap_map[swp_offset(entry)]))) { > - put_swap_device(p); > - return 0; > - } > + si = get_swap_device(entry); > + if (!si) > + return; > > - count = __swap_entry_free(p, entry); > - if (count == SWAP_HAS_CACHE) > - __try_to_reclaim_swap(p, swp_offset(entry), > + if (WARN_ON(end > si->max)) > + goto out; > + > + /* > + * First free all entries in the range. > + */ > + for (offset = swp_offset(entry); offset < end; offset++) { > + if (!WARN_ON(data_race(!si->swap_map[offset]))) > + __swap_entry_free(si, swp_entry(type, offset)); > + } > + > + /* > + * Now go back over the range trying to reclaim the swap cache. This is > + * more efficient for large folios because we will only try to reclaim > + * the swap once per folio in the common case. If we do > + * __swap_entry_free() and __try_to_reclaim_swap() in the same loop, the > + * latter will get a reference and lock the folio for every individual > + * page but will only succeed once the swap slot for every subpage is > + * zero. > + */ > + for (offset = swp_offset(entry); offset < end; offset += nr) { > + nr = 1; > + if (READ_ONCE(si->swap_map[offset]) == SWAP_HAS_CACHE) { > + /* > + * Folios are always naturally aligned in swap so > + * advance forward to the next boundary. Zero means no > + * folio was found for the swap entry, so advance by 1 > + * in this case. Negative value means folio was found > + * but could not be reclaimed. Here we can still advance > + * to the next boundary. > + */ > + nr = __try_to_reclaim_swap(si, offset, > TTRS_UNMAPPED | TTRS_FULL); > - put_swap_device(p); > + if (nr == 0) > + nr = 1; > + else if (nr < 0) > + nr = -nr; > + nr = ALIGN(offset + 1, nr) - offset; > + } > } > - return p != NULL; > + > +out: > + put_swap_device(si); > } > > #ifdef CONFIG_HIBERNATION
On 20.03.24 12:10, Ryan Roberts wrote: > Hi David, I'm usually lazy with review during the merge window :P > > I hate to chase, but since you provided feedback on a couple of the other > patches in the series, I wondered if you missed this one? It's the one that does > the batching of free_swap_and_cache(), which you suggested in order to prevent > needlessly taking folio locks and refs. > > If you have any feedback, it would be appreciated, otherwise I'm planning to > repost as-is next week (nobody else has posted comments against this patch > either) as part of the updated series. On my TODO list!
On 20/03/2024 14:13, David Hildenbrand wrote: > On 20.03.24 12:10, Ryan Roberts wrote: >> Hi David, > > I'm usually lazy with review during the merge window :P Ahh no worries! I'll send out the latest version next week, and can go from there. > >> >> I hate to chase, but since you provided feedback on a couple of the other >> patches in the series, I wondered if you missed this one? It's the one that does >> the batching of free_swap_and_cache(), which you suggested in order to prevent >> needlessly taking folio locks and refs. >> >> If you have any feedback, it would be appreciated, otherwise I'm planning to >> repost as-is next week (nobody else has posted comments against this patch >> either) as part of the updated series. > > On my TODO list! >
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 85fc7554cd52..8cf1f2fe2c25 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -708,6 +708,34 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm, } #endif +#ifndef clear_not_present_full_ptes +/** + * clear_not_present_full_ptes - Clear consecutive not present PTEs. + * @mm: Address space the ptes represent. + * @addr: Address of the first pte. + * @ptep: Page table pointer for the first entry. + * @nr: Number of entries to clear. + * @full: Whether we are clearing a full mm. + * + * May be overridden by the architecture; otherwise, implemented as a simple + * loop over pte_clear_not_present_full(). + * + * Context: The caller holds the page table lock. The PTEs are all not present. + * The PTEs are all in the same PMD. + */ +static inline void clear_not_present_full_ptes(struct mm_struct *mm, + unsigned long addr, pte_t *ptep, unsigned int nr, int full) +{ + for (;;) { + pte_clear_not_present_full(mm, addr, ptep, full); + if (--nr == 0) + break; + ptep++; + addr += PAGE_SIZE; + } +} +#endif + #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH extern pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address, diff --git a/include/linux/swap.h b/include/linux/swap.h index 4a8b6c60793a..f2b7f204b968 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -481,7 +481,7 @@ extern int swap_duplicate(swp_entry_t); extern int swapcache_prepare(swp_entry_t); extern void swap_free(swp_entry_t); extern void swapcache_free_entries(swp_entry_t *entries, int n); -extern int free_swap_and_cache(swp_entry_t); +extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); int swap_type_of(dev_t device, sector_t offset); int find_first_swap(dev_t *device); extern unsigned int count_swap_pages(int, int); @@ -530,8 +530,9 @@ static inline void put_swap_device(struct swap_info_struct *si) #define free_pages_and_swap_cache(pages, nr) \ release_pages((pages), (nr)); -/* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */ -#define free_swap_and_cache(e) is_pfn_swap_entry(e) +static inline void free_swap_and_cache_nr(swp_entry_t entry, int nr) +{ +} static inline void free_swap_cache(struct folio *folio) { @@ -599,6 +600,11 @@ static inline int add_swap_extent(struct swap_info_struct *sis, } #endif /* CONFIG_SWAP */ +static inline void free_swap_and_cache(swp_entry_t entry) +{ + free_swap_and_cache_nr(entry, 1); +} + #ifdef CONFIG_MEMCG static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) { diff --git a/mm/internal.h b/mm/internal.h index a3e19194079f..8dbb1335df88 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -11,6 +11,8 @@ #include <linux/mm.h> #include <linux/pagemap.h> #include <linux/rmap.h> +#include <linux/swap.h> +#include <linux/swapops.h> #include <linux/tracepoint-defs.h> struct folio_batch; @@ -174,6 +176,52 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, return min(ptep - start_ptep, max_nr); } + +/** + * swap_pte_batch - detect a PTE batch for a set of contiguous swap entries + * @start_ptep: Page table pointer for the first entry. + * @max_nr: The maximum number of table entries to consider. + * @entry: Swap entry recovered from the first table entry. + * + * Detect a batch of contiguous swap entries: consecutive (non-present) PTEs + * containing swap entries all with consecutive offsets and targeting the same + * swap type. + * + * max_nr must be at least one and must be limited by the caller so scanning + * cannot exceed a single page table. + * + * Return: the number of table entries in the batch. + */ +static inline int swap_pte_batch(pte_t *start_ptep, int max_nr, + swp_entry_t entry) +{ + const pte_t *end_ptep = start_ptep + max_nr; + unsigned long expected_offset = swp_offset(entry) + 1; + unsigned int expected_type = swp_type(entry); + pte_t *ptep = start_ptep + 1; + + VM_WARN_ON(max_nr < 1); + VM_WARN_ON(non_swap_entry(entry)); + + while (ptep < end_ptep) { + pte_t pte = ptep_get(ptep); + + if (pte_none(pte) || pte_present(pte)) + break; + + entry = pte_to_swp_entry(pte); + + if (non_swap_entry(entry) || + swp_type(entry) != expected_type || + swp_offset(entry) != expected_offset) + break; + + expected_offset++; + ptep++; + } + + return ptep - start_ptep; +} #endif /* CONFIG_MMU */ void __acct_reclaim_writeback(pg_data_t *pgdat, struct folio *folio, diff --git a/mm/madvise.c b/mm/madvise.c index 44a498c94158..547dcd1f7a39 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -628,6 +628,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, struct folio *folio; int nr_swap = 0; unsigned long next; + int nr, max_nr; next = pmd_addr_end(addr, end); if (pmd_trans_huge(*pmd)) @@ -640,7 +641,8 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, return 0; flush_tlb_batched_pending(mm); arch_enter_lazy_mmu_mode(); - for (; addr != end; pte++, addr += PAGE_SIZE) { + for (; addr != end; pte += nr, addr += PAGE_SIZE * nr) { + nr = 1; ptent = ptep_get(pte); if (pte_none(ptent)) @@ -655,9 +657,11 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, entry = pte_to_swp_entry(ptent); if (!non_swap_entry(entry)) { - nr_swap--; - free_swap_and_cache(entry); - pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); + max_nr = (end - addr) / PAGE_SIZE; + nr = swap_pte_batch(pte, max_nr, entry); + nr_swap -= nr; + free_swap_and_cache_nr(entry, nr); + clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm); } else if (is_hwpoison_entry(entry) || is_poisoned_swp_entry(entry)) { pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); diff --git a/mm/memory.c b/mm/memory.c index f2bc6dd15eb8..25c0ef1c7ff3 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1629,12 +1629,13 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, folio_remove_rmap_pte(folio, page, vma); folio_put(folio); } else if (!non_swap_entry(entry)) { - /* Genuine swap entry, hence a private anon page */ + max_nr = (end - addr) / PAGE_SIZE; + nr = swap_pte_batch(pte, max_nr, entry); + /* Genuine swap entries, hence a private anon pages */ if (!should_zap_cows(details)) continue; - rss[MM_SWAPENTS]--; - if (unlikely(!free_swap_and_cache(entry))) - print_bad_pte(vma, addr, ptent, NULL); + rss[MM_SWAPENTS] -= nr; + free_swap_and_cache_nr(entry, nr); } else if (is_migration_entry(entry)) { folio = pfn_swap_entry_folio(entry); if (!should_zap_folio(details, folio)) @@ -1657,8 +1658,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, pr_alert("unrecognized swap entry 0x%lx\n", entry.val); WARN_ON_ONCE(1); } - pte_clear_not_present_full(mm, addr, pte, tlb->fullmm); - zap_install_uffd_wp_if_needed(vma, addr, pte, 1, details, ptent); + clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm); + zap_install_uffd_wp_if_needed(vma, addr, pte, nr, details, ptent); } while (pte += nr, addr += PAGE_SIZE * nr, addr != end); add_mm_rss_vec(mm, rss); diff --git a/mm/swapfile.c b/mm/swapfile.c index df1de034f6d8..ee7e44cb40c5 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -130,7 +130,11 @@ static inline unsigned char swap_count(unsigned char ent) /* Reclaim the swap entry if swap is getting full*/ #define TTRS_FULL 0x4 -/* returns 1 if swap entry is freed */ +/* + * returns number of pages in the folio that backs the swap entry. If positive, + * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no + * folio was associated with the swap entry. + */ static int __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset, unsigned long flags) { @@ -155,6 +159,7 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si, ret = folio_free_swap(folio); folio_unlock(folio); } + ret = ret ? folio_nr_pages(folio) : -folio_nr_pages(folio); folio_put(folio); return ret; } @@ -895,7 +900,7 @@ static int scan_swap_map_slots(struct swap_info_struct *si, swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY); spin_lock(&si->lock); /* entry was freed successfully, try to use this again */ - if (swap_was_freed) + if (swap_was_freed > 0) goto checks; goto scan; /* check next one */ } @@ -1572,32 +1577,63 @@ bool folio_free_swap(struct folio *folio) return true; } -/* - * Free the swap entry like above, but also try to - * free the page cache entry if it is the last user. - */ -int free_swap_and_cache(swp_entry_t entry) +void free_swap_and_cache_nr(swp_entry_t entry, int nr) { - struct swap_info_struct *p; - unsigned char count; + unsigned long end = swp_offset(entry) + nr; + unsigned int type = swp_type(entry); + struct swap_info_struct *si; + unsigned long offset; if (non_swap_entry(entry)) - return 1; + return; - p = get_swap_device(entry); - if (p) { - if (WARN_ON(data_race(!p->swap_map[swp_offset(entry)]))) { - put_swap_device(p); - return 0; - } + si = get_swap_device(entry); + if (!si) + return; - count = __swap_entry_free(p, entry); - if (count == SWAP_HAS_CACHE) - __try_to_reclaim_swap(p, swp_offset(entry), + if (WARN_ON(end > si->max)) + goto out; + + /* + * First free all entries in the range. + */ + for (offset = swp_offset(entry); offset < end; offset++) { + if (!WARN_ON(data_race(!si->swap_map[offset]))) + __swap_entry_free(si, swp_entry(type, offset)); + } + + /* + * Now go back over the range trying to reclaim the swap cache. This is + * more efficient for large folios because we will only try to reclaim + * the swap once per folio in the common case. If we do + * __swap_entry_free() and __try_to_reclaim_swap() in the same loop, the + * latter will get a reference and lock the folio for every individual + * page but will only succeed once the swap slot for every subpage is + * zero. + */ + for (offset = swp_offset(entry); offset < end; offset += nr) { + nr = 1; + if (READ_ONCE(si->swap_map[offset]) == SWAP_HAS_CACHE) { + /* + * Folios are always naturally aligned in swap so + * advance forward to the next boundary. Zero means no + * folio was found for the swap entry, so advance by 1 + * in this case. Negative value means folio was found + * but could not be reclaimed. Here we can still advance + * to the next boundary. + */ + nr = __try_to_reclaim_swap(si, offset, TTRS_UNMAPPED | TTRS_FULL); - put_swap_device(p); + if (nr == 0) + nr = 1; + else if (nr < 0) + nr = -nr; + nr = ALIGN(offset + 1, nr) - offset; + } } - return p != NULL; + +out: + put_swap_device(si); } #ifdef CONFIG_HIBERNATION
Now that we no longer have a convenient flag in the cluster to determine if a folio is large, free_swap_and_cache() will take a reference and lock a large folio much more often, which could lead to contention and (e.g.) failure to split large folios, etc. Let's solve that problem by batch freeing swap and cache with a new function, free_swap_and_cache_nr(), to free a contiguous range of swap entries together. This allows us to first drop a reference to each swap slot before we try to release the cache folio. This means we only try to release the folio once, only taking the reference and lock once - much better than the previous 512 times for the 2M THP case. Contiguous swap entries are gathered in zap_pte_range() and madvise_free_pte_range() in a similar way to how present ptes are already gathered in zap_pte_range(). While we are at it, let's simplify by converting the return type of both functions to void. The return value was used only by zap_pte_range() to print a bad pte, and was ignored by everyone else, so the extra reporting wasn't exactly guaranteed. We will still get the warning with most of the information from get_swap_device(). With the batch version, we wouldn't know which pte was bad anyway so could print the wrong one. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> --- include/linux/pgtable.h | 28 +++++++++++++++ include/linux/swap.h | 12 +++++-- mm/internal.h | 48 +++++++++++++++++++++++++ mm/madvise.c | 12 ++++--- mm/memory.c | 13 +++---- mm/swapfile.c | 78 ++++++++++++++++++++++++++++++----------- 6 files changed, 157 insertions(+), 34 deletions(-)