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Message-ID: <15a0a23a-54ad-71d3-d519-0750981a81b5@nvidia.com>
Date: Mon, 8 Mar 2021 10:24:45 -0800
From: Ralph Campbell <rcampbell@...dia.com>
To: Alistair Popple <apopple@...dia.com>, <linux-mm@...ck.org>,
<nouveau@...ts.freedesktop.org>, <bskeggs@...hat.com>,
<akpm@...ux-foundation.org>
CC: <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<kvm-ppc@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
<jhubbard@...dia.com>, <jglisse@...hat.com>
Subject: Re: [PATCH v4 1/8] mm: Remove special swap entry functions
On 3/3/21 10:16 PM, Alistair Popple wrote:
> Remove the migration and device private entry_to_page() and
> entry_to_pfn() inline functions and instead open code them directly.
> This results in shorter code which is easier to understand.
>
> Signed-off-by: Alistair Popple <apopple@...dia.com>
Looks OK to me.
Reviewed-by: Ralph Campbell <rcampbell@...dia.com>
> ---
>
> v4:
> * Added pfn_swap_entry_to_page()
> * Reinstated check that migration entries point to locked pages
> * Removed #define swapcache_prepare which isn't needed for CONFIG_SWAP=0
> builds
> ---
> arch/s390/mm/pgtable.c | 2 +-
> fs/proc/task_mmu.c | 23 +++++---------
> include/linux/swap.h | 4 +--
> include/linux/swapops.h | 69 ++++++++++++++---------------------------
> mm/hmm.c | 5 ++-
> mm/huge_memory.c | 4 +--
> mm/memcontrol.c | 2 +-
> mm/memory.c | 10 +++---
> mm/migrate.c | 6 ++--
> mm/page_vma_mapped.c | 6 ++--
> 10 files changed, 50 insertions(+), 81 deletions(-)
>
> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
> index 18205f851c24..aae001096c46 100644
> --- a/arch/s390/mm/pgtable.c
> +++ b/arch/s390/mm/pgtable.c
> @@ -691,7 +691,7 @@ static void ptep_zap_swap_entry(struct mm_struct *mm, swp_entry_t entry)
> if (!non_swap_entry(entry))
> dec_mm_counter(mm, MM_SWAPENTS);
> else if (is_migration_entry(entry)) {
> - struct page *page = migration_entry_to_page(entry);
> + struct page *page = pfn_swap_entry_to_page(entry));
>
> dec_mm_counter(mm, mm_counter(page));
> }
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 602e3a52884d..7c75af0fc423 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -514,10 +514,8 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> } else {
> mss->swap_pss += (u64)PAGE_SIZE << PSS_SHIFT;
> }
> - } else if (is_migration_entry(swpent))
> - page = migration_entry_to_page(swpent);
> - else if (is_device_private_entry(swpent))
> - page = device_private_entry_to_page(swpent);
> + } else if (is_pfn_swap_entry(swpent))
> + page = pfn_swap_entry_to_page(swpent);
> } else if (unlikely(IS_ENABLED(CONFIG_SHMEM) && mss->check_shmem_swap
> && pte_none(*pte))) {
> page = xa_load(&vma->vm_file->f_mapping->i_pages,
> @@ -549,7 +547,7 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
> swp_entry_t entry = pmd_to_swp_entry(*pmd);
>
> if (is_migration_entry(entry))
> - page = migration_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
> }
> if (IS_ERR_OR_NULL(page))
> return;
> @@ -691,10 +689,8 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
> } else if (is_swap_pte(*pte)) {
> swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> - if (is_migration_entry(swpent))
> - page = migration_entry_to_page(swpent);
> - else if (is_device_private_entry(swpent))
> - page = device_private_entry_to_page(swpent);
> + if (is_pfn_swap_entry(swpent))
> + page = pfn_swap_entry_to_page(swpent);
> }
> if (page) {
> int mapcount = page_mapcount(page);
> @@ -1382,11 +1378,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
> frame = swp_type(entry) |
> (swp_offset(entry) << MAX_SWAPFILES_SHIFT);
> flags |= PM_SWAP;
> - if (is_migration_entry(entry))
> - page = migration_entry_to_page(entry);
> -
> - if (is_device_private_entry(entry))
> - page = device_private_entry_to_page(entry);
> + if (is_pfn_swap_entry(entry))
> + page = pfn_swap_entry_to_page(entry);
> }
>
> if (page && !PageAnon(page))
> @@ -1443,7 +1436,7 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
> if (pmd_swp_soft_dirty(pmd))
> flags |= PM_SOFT_DIRTY;
> VM_BUG_ON(!is_pmd_migration_entry(pmd));
> - page = migration_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
> }
> #endif
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 596bc2f4d9b0..57a7690966a4 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -519,8 +519,8 @@ static inline void show_swap_cache_info(void)
> {
> }
>
> -#define free_swap_and_cache(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
> -#define swapcache_prepare(e) ({(is_migration_entry(e) || is_device_private_entry(e));})
> +/* 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 int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
> {
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index d9b7c9132c2f..3fd88081107c 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -121,16 +121,6 @@ static inline bool is_write_device_private_entry(swp_entry_t entry)
> {
> return unlikely(swp_type(entry) == SWP_DEVICE_WRITE);
> }
> -
> -static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry)
> -{
> - return swp_offset(entry);
> -}
> -
> -static inline struct page *device_private_entry_to_page(swp_entry_t entry)
> -{
> - return pfn_to_page(swp_offset(entry));
> -}
> #else /* CONFIG_DEVICE_PRIVATE */
> static inline swp_entry_t make_device_private_entry(struct page *page, bool write)
> {
> @@ -150,16 +140,6 @@ static inline bool is_write_device_private_entry(swp_entry_t entry)
> {
> return false;
> }
> -
> -static inline unsigned long device_private_entry_to_pfn(swp_entry_t entry)
> -{
> - return 0;
> -}
> -
> -static inline struct page *device_private_entry_to_page(swp_entry_t entry)
> -{
> - return NULL;
> -}
> #endif /* CONFIG_DEVICE_PRIVATE */
>
> #ifdef CONFIG_MIGRATION
> @@ -182,22 +162,6 @@ static inline int is_write_migration_entry(swp_entry_t entry)
> return unlikely(swp_type(entry) == SWP_MIGRATION_WRITE);
> }
>
> -static inline unsigned long migration_entry_to_pfn(swp_entry_t entry)
> -{
> - return swp_offset(entry);
> -}
> -
> -static inline struct page *migration_entry_to_page(swp_entry_t entry)
> -{
> - struct page *p = pfn_to_page(swp_offset(entry));
> - /*
> - * Any use of migration entries may only occur while the
> - * corresponding page is locked
> - */
> - BUG_ON(!PageLocked(compound_head(p)));
> - return p;
> -}
> -
> static inline void make_migration_entry_read(swp_entry_t *entry)
> {
> *entry = swp_entry(SWP_MIGRATION_READ, swp_offset(*entry));
> @@ -217,16 +181,6 @@ static inline int is_migration_entry(swp_entry_t swp)
> return 0;
> }
>
> -static inline unsigned long migration_entry_to_pfn(swp_entry_t entry)
> -{
> - return 0;
> -}
> -
> -static inline struct page *migration_entry_to_page(swp_entry_t entry)
> -{
> - return NULL;
> -}
> -
> static inline void make_migration_entry_read(swp_entry_t *entryp) { }
> static inline void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> spinlock_t *ptl) { }
> @@ -241,6 +195,29 @@ static inline int is_write_migration_entry(swp_entry_t entry)
>
> #endif
>
> +static inline struct page *pfn_swap_entry_to_page(swp_entry_t entry)
> +{
> + struct page *p = pfn_to_page(swp_offset(entry));
> +
> + /*
> + * Any use of migration entries may only occur while the
> + * corresponding page is locked
> + */
> + BUG_ON(is_migration_entry(entry) && !PageLocked(compound_head(p)));
> +
> + return p;
> +}
> +
> +/*
> + * A pfn swap entry is a special type of swap entry that always has a pfn stored
> + * in the swap offset. They are used to represent unaddressable device memory
> + * and to restrict access to a page undergoing migration.
> + */
> +static inline bool is_pfn_swap_entry(swp_entry_t entry)
> +{
> + return is_migration_entry(entry) || is_device_private_entry(entry);
> +}
> +
> struct page_vma_mapped_walk;
>
> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 943cb2ba4442..3b2dda71d0ed 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -214,7 +214,7 @@ static inline bool hmm_is_device_private_entry(struct hmm_range *range,
> swp_entry_t entry)
> {
> return is_device_private_entry(entry) &&
> - device_private_entry_to_page(entry)->pgmap->owner ==
> + pfn_swap_entry_to_page(entry)->pgmap->owner ==
> range->dev_private_owner;
> }
>
> @@ -257,8 +257,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
> cpu_flags = HMM_PFN_VALID;
> if (is_write_device_private_entry(entry))
> cpu_flags |= HMM_PFN_WRITE;
> - *hmm_pfn = device_private_entry_to_pfn(entry) |
> - cpu_flags;
> + *hmm_pfn = swp_offset(entry) | cpu_flags;
> return 0;
> }
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 91ca9b103ee5..d65eebf446ae 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1695,7 +1695,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>
> VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
> entry = pmd_to_swp_entry(orig_pmd);
> - page = pfn_to_page(swp_offset(entry));
> + page = pfn_swap_entry_to_page(entry);
> flush_needed = 0;
> } else
> WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
> @@ -2103,7 +2103,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> swp_entry_t entry;
>
> entry = pmd_to_swp_entry(old_pmd);
> - page = pfn_to_page(swp_offset(entry));
> + page = pfn_swap_entry_to_page(entry);
> write = is_write_migration_entry(entry);
> young = false;
> soft_dirty = pmd_swp_soft_dirty(old_pmd);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 913c2b9e5c72..9fa9ec9d0ace 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5544,7 +5544,7 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
> * as special swap entry in the CPU page table.
> */
> if (is_device_private_entry(ent)) {
> - page = device_private_entry_to_page(ent);
> + page = pfn_swap_entry_to_page(ent);
> /*
> * MEMORY_DEVICE_PRIVATE means ZONE_DEVICE page and which have
> * a refcount of 1 when free (unlike normal page)
> diff --git a/mm/memory.c b/mm/memory.c
> index feff48e1465a..99a6a695b1b1 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -718,7 +718,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> }
> rss[MM_SWAPENTS]++;
> } else if (is_migration_entry(entry)) {
> - page = migration_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
>
> rss[mm_counter(page)]++;
>
> @@ -737,7 +737,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> set_pte_at(src_mm, addr, src_pte, pte);
> }
> } else if (is_device_private_entry(entry)) {
> - page = device_private_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
>
> /*
> * Update rss count even for unaddressable pages, as
> @@ -1274,7 +1274,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
>
> entry = pte_to_swp_entry(ptent);
> if (is_device_private_entry(entry)) {
> - struct page *page = device_private_entry_to_page(entry);
> + struct page *page = pfn_swap_entry_to_page(entry);
>
> if (unlikely(details && details->check_mapping)) {
> /*
> @@ -1303,7 +1303,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
> else if (is_migration_entry(entry)) {
> struct page *page;
>
> - page = migration_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
> rss[mm_counter(page)]--;
> }
> if (unlikely(!free_swap_and_cache(entry)))
> @@ -3271,7 +3271,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> migration_entry_wait(vma->vm_mm, vmf->pmd,
> vmf->address);
> } else if (is_device_private_entry(entry)) {
> - vmf->page = device_private_entry_to_page(entry);
> + vmf->page = pfn_swap_entry_to_page(entry);
> ret = vmf->page->pgmap->ops->migrate_to_ram(vmf);
> } else if (is_hwpoison_entry(entry)) {
> ret = VM_FAULT_HWPOISON;
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 20ca887ea769..39246907eac3 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -321,7 +321,7 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> if (!is_migration_entry(entry))
> goto out;
>
> - page = migration_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
>
> /*
> * Once page cache replacement of page migration started, page_count
> @@ -361,7 +361,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
> ptl = pmd_lock(mm, pmd);
> if (!is_pmd_migration_entry(*pmd))
> goto unlock;
> - page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
> + page = pfn_swap_entry_to_page(pmd_to_swp_entry(*pmd));
> if (!get_page_unless_zero(page))
> goto unlock;
> spin_unlock(ptl);
> @@ -2437,7 +2437,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> if (!is_device_private_entry(entry))
> goto next;
>
> - page = device_private_entry_to_page(entry);
> + page = pfn_swap_entry_to_page(entry);
> if (!(migrate->flags &
> MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
> page->pgmap->owner != migrate->pgmap_owner)
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index 86e3a3688d59..eed988ab2e81 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -96,7 +96,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
> if (!is_migration_entry(entry))
> return false;
>
> - pfn = migration_entry_to_pfn(entry);
> + pfn = swp_offset(entry);
> } else if (is_swap_pte(*pvmw->pte)) {
> swp_entry_t entry;
>
> @@ -105,7 +105,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
> if (!is_device_private_entry(entry))
> return false;
>
> - pfn = device_private_entry_to_pfn(entry);
> + pfn = swp_offset(entry);
> } else {
> if (!pte_present(*pvmw->pte))
> return false;
> @@ -200,7 +200,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> if (is_migration_entry(pmd_to_swp_entry(*pvmw->pmd))) {
> swp_entry_t entry = pmd_to_swp_entry(*pvmw->pmd);
>
> - if (migration_entry_to_page(entry) != page)
> + if (pfn_swap_entry_to_page(entry) != page)
> return not_found(pvmw);
> return true;
> }
>
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