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Wed, 27 Mar 2024 07:45:50 -0700 (PDT) From: Ryan Roberts To: Andrew Morton , David Hildenbrand , Matthew Wilcox , Huang Ying , Gao Xiang , Yu Zhao , Yang Shi , Michal Hocko , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Chris Li , Lance Yang Cc: Ryan Roberts , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v5 2/6] mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache() Date: Wed, 27 Mar 2024 14:45:33 +0000 Message-Id: <20240327144537.4165578-3-ryan.roberts@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20240327144537.4165578-1-ryan.roberts@arm.com> References: <20240327144537.4165578-1-ryan.roberts@arm.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: A197110002C X-Rspam-User: X-Stat-Signature: cybjtuhqs8a7h7a9e4639g35gtjcimug X-Rspamd-Server: rspam01 X-HE-Tag: 1711550753-422590 X-HE-Meta: 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 3BOWv64e ZxyKyDuuUK5i87sUKQOkmQFCLCGeTvyb9Dt+wt8gX0tC22Qsn548fznUJ6vYTdCy/tBo87N1qwWEna+Xg6zibr3ZRez8EEOGObCCveg+sue1Q/XZdBbuypBcZZ94IrhXrVz2/ddFCrLRu+Kr8ogAdo/dFv8KFdGW0Rztq9OCwXiTiwYVboHeyx7bdLuXoeh9soN2AFFj6CEdAEPs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 --- 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 09c85c7bf9c2..8185939df1e8 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 f6f78198f000..5737236dc3ce 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -471,7 +471,7 @@ 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); @@ -520,8 +520,9 @@ 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) { @@ -589,6 +590,11 @@ 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 8e11f7b2da21..eadb79c3a357 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -11,6 +11,8 @@ #include #include #include +#include +#include #include struct folio_batch; @@ -189,6 +191,52 @@ 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 1f77a51baaac..070bedb4996e 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 36191a9c799c..9d844582ba38 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1631,12 +1631,13 @@ 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)) @@ -1659,8 +1660,8 @@ 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 0d44ee2b4f9c..cedfc82d37e5 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