Re: [PATCH RFC 1/3] mm/gup: consistently name GUP-fast functions

From: Mike Rapoport
Date: Wed Mar 27 2024 - 11:13:53 EST

On Wed, Mar 27, 2024 at 02:05:36PM +0100, David Hildenbrand wrote:
> Let's consistently call the "fast-only" part of GUP "GUP-fast" and rename
> all relevant internal functions to start with "gup_fast", to make it
> clearer that this is not ordinary GUP. The current mixture of
> "lockless", "gup" and "gup_fast" is confusing.
>
> Further, avoid the term "huge" when talking about a "leaf" -- for
> example, we nowadays check pmd_leaf() because pmd_huge() is gone. For the
> "hugepd"/"hugepte" stuff, it's part of the name ("is_hugepd"), so that
> says.

typo: stays

> What remains is the "external" interface:
> * get_user_pages_fast_only()
> * get_user_pages_fast()
> * pin_user_pages_fast()
>
> And the "internal" interface that handles GUP-fast + fallback:
> * internal_get_user_pages_fast()
>
> The high-level internal function for GUP-fast is now:
> * gup_fast()
>
> The basic GUP-fast walker functions:
> * gup_pgd_range() -> gup_fast_pgd_range()
> * gup_p4d_range() -> gup_fast_p4d_range()
> * gup_pud_range() -> gup_fast_pud_range()
> * gup_pmd_range() -> gup_fast_pmd_range()
> * gup_pte_range() -> gup_fast_pte_range()
> * gup_huge_pgd() -> gup_fast_pgd_leaf()
> * gup_huge_pud() -> gup_fast_pud_leaf()
> * gup_huge_pmd() -> gup_fast_pmd_leaf()
>
> The weird hugepd stuff:
> * gup_huge_pd() -> gup_fast_hugepd()
> * gup_hugepte() -> gup_fast_hugepte()
>
> The weird devmap stuff:
> * __gup_device_huge_pud() -> gup_fast_devmap_pud_leaf()
> * __gup_device_huge_pmd -> gup_fast_devmap_pmd_leaf()
> * __gup_device_huge() -> gup_fast_devmap_leaf()
>
> Helper functions:
> * unpin_user_pages_lockless() -> gup_fast_unpin_user_pages()
> * gup_fast_folio_allowed() is already properly named
> * gup_fast_permitted() is already properly named
>
> With "gup_fast()", we now even have a function that is referred to in
> comment in mm/mmu_gather.c.
>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>

> ---
> mm/gup.c | 164 ++++++++++++++++++++++++++++---------------------------
> 1 file changed, 84 insertions(+), 80 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 03b74b148e30..c293aff30c5d 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -440,7 +440,7 @@ void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
> }
> EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
>
> -static void unpin_user_pages_lockless(struct page **pages, unsigned long npages)
> +static void gup_fast_unpin_user_pages(struct page **pages, unsigned long npages)
> {
> unsigned long i;
> struct folio *folio;
> @@ -2431,7 +2431,7 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
> EXPORT_SYMBOL(get_user_pages_unlocked);
>
> /*
> - * Fast GUP
> + * GUP-fast
> *
> * get_user_pages_fast attempts to pin user pages by walking the page
> * tables directly and avoids taking locks. Thus the walker needs to be
> @@ -2445,7 +2445,7 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
> *
> * Another way to achieve this is to batch up page table containing pages
> * belonging to more than one mm_user, then rcu_sched a callback to free those
> - * pages. Disabling interrupts will allow the fast_gup walker to both block
> + * pages. Disabling interrupts will allow the gup_fast() walker to both block
> * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
> * (which is a relatively rare event). The code below adopts this strategy.
> *
> @@ -2589,9 +2589,9 @@ static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
> * also check pmd here to make sure pmd doesn't change (corresponds to
> * pmdp_collapse_flush() in the THP collapse code path).
> */
> -static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> struct dev_pagemap *pgmap = NULL;
> int nr_start = *nr, ret = 0;
> @@ -2688,20 +2688,19 @@ static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
> *
> * For a futex to be placed on a THP tail page, get_futex_key requires a
> * get_user_pages_fast_only implementation that can pin pages. Thus it's still
> - * useful to have gup_huge_pmd even if we can't operate on ptes.
> + * useful to have gup_fast_pmd_leaf even if we can't operate on ptes.
> */
> -static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> return 0;
> }
> #endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
>
> #if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
> -static int __gup_device_huge(unsigned long pfn, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_devmap_leaf(unsigned long pfn, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages, int *nr)
> {
> int nr_start = *nr;
> struct dev_pagemap *pgmap = NULL;
> @@ -2734,15 +2733,15 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
> return addr == end;
> }
>
> -static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_devmap_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> unsigned long fault_pfn;
> int nr_start = *nr;
>
> fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
> + if (!gup_fast_devmap_leaf(fault_pfn, addr, end, flags, pages, nr))
> return 0;
>
> if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
> @@ -2752,15 +2751,15 @@ static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> return 1;
> }
>
> -static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_devmap_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> unsigned long fault_pfn;
> int nr_start = *nr;
>
> fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> - if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
> + if (!gup_fast_devmap_leaf(fault_pfn, addr, end, flags, pages, nr))
> return 0;
>
> if (unlikely(pud_val(orig) != pud_val(*pudp))) {
> @@ -2770,17 +2769,17 @@ static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> return 1;
> }
> #else
> -static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_devmap_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> BUILD_BUG();
> return 0;
> }
>
> -static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_devmap_pud_leaf(pud_t pud, pud_t *pudp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> BUILD_BUG();
> return 0;
> @@ -2806,9 +2805,9 @@ static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
> return (__boundary - 1 < end - 1) ? __boundary : end;
> }
>
> -static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> unsigned long pte_end;
> struct page *page;
> @@ -2855,7 +2854,7 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
> return 1;
> }
>
> -static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
> +static int gup_fast_hugepd(hugepd_t hugepd, unsigned long addr,
> unsigned int pdshift, unsigned long end, unsigned int flags,
> struct page **pages, int *nr)
> {
> @@ -2866,14 +2865,14 @@ static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
> ptep = hugepte_offset(hugepd, addr, pdshift);
> do {
> next = hugepte_addr_end(addr, end, sz);
> - if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
> + if (!gup_fast_hugepte(ptep, sz, addr, end, flags, pages, nr))
> return 0;
> } while (ptep++, addr = next, addr != end);
>
> return 1;
> }
> #else
> -static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
> +static inline int gup_fast_hugepd(hugepd_t hugepd, unsigned long addr,
> unsigned int pdshift, unsigned long end, unsigned int flags,
> struct page **pages, int *nr)
> {
> @@ -2881,9 +2880,9 @@ static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
> }
> #endif /* CONFIG_ARCH_HAS_HUGEPD */
>
> -static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> struct page *page;
> struct folio *folio;
> @@ -2895,8 +2894,8 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> if (pmd_devmap(orig)) {
> if (unlikely(flags & FOLL_LONGTERM))
> return 0;
> - return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
> - pages, nr);
> + return gup_fast_devmap_pmd_leaf(orig, pmdp, addr, end, flags,
> + pages, nr);
> }
>
> page = nth_page(pmd_page(orig), (addr & ~PMD_MASK) >> PAGE_SHIFT);
> @@ -2925,9 +2924,9 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> return 1;
> }
>
> -static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_pud_leaf(pud_t orig, pud_t *pudp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> struct page *page;
> struct folio *folio;
> @@ -2939,8 +2938,8 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> if (pud_devmap(orig)) {
> if (unlikely(flags & FOLL_LONGTERM))
> return 0;
> - return __gup_device_huge_pud(orig, pudp, addr, end, flags,
> - pages, nr);
> + return gup_fast_devmap_pud_leaf(orig, pudp, addr, end, flags,
> + pages, nr);
> }
>
> page = nth_page(pud_page(orig), (addr & ~PUD_MASK) >> PAGE_SHIFT);
> @@ -2970,9 +2969,9 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> return 1;
> }
>
> -static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> - unsigned long end, unsigned int flags,
> - struct page **pages, int *nr)
> +static int gup_fast_pgd_leaf(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> int refs;
> struct page *page;
> @@ -3010,8 +3009,9 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
> return 1;
> }
>
> -static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned long end,
> - unsigned int flags, struct page **pages, int *nr)
> +static int gup_fast_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> unsigned long next;
> pmd_t *pmdp;
> @@ -3025,11 +3025,11 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo
> return 0;
>
> if (unlikely(pmd_leaf(pmd))) {
> - /* See gup_pte_range() */
> + /* See gup_fast_pte_range() */
> if (pmd_protnone(pmd))
> return 0;
>
> - if (!gup_huge_pmd(pmd, pmdp, addr, next, flags,
> + if (!gup_fast_pmd_leaf(pmd, pmdp, addr, next, flags,
> pages, nr))
> return 0;
>
> @@ -3038,18 +3038,20 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo
> * architecture have different format for hugetlbfs
> * pmd format and THP pmd format
> */
> - if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
> - PMD_SHIFT, next, flags, pages, nr))
> + if (!gup_fast_hugepd(__hugepd(pmd_val(pmd)), addr,
> + PMD_SHIFT, next, flags, pages, nr))
> return 0;
> - } else if (!gup_pte_range(pmd, pmdp, addr, next, flags, pages, nr))
> + } else if (!gup_fast_pte_range(pmd, pmdp, addr, next, flags,
> + pages, nr))
> return 0;
> } while (pmdp++, addr = next, addr != end);
>
> return 1;
> }
>
> -static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned long end,
> - unsigned int flags, struct page **pages, int *nr)
> +static int gup_fast_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> unsigned long next;
> pud_t *pudp;
> @@ -3062,22 +3064,24 @@ static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned lo
> if (unlikely(!pud_present(pud)))
> return 0;
> if (unlikely(pud_leaf(pud))) {
> - if (!gup_huge_pud(pud, pudp, addr, next, flags,
> - pages, nr))
> + if (!gup_fast_pud_leaf(pud, pudp, addr, next, flags,
> + pages, nr))
> return 0;
> } else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
> - if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
> - PUD_SHIFT, next, flags, pages, nr))
> + if (!gup_fast_hugepd(__hugepd(pud_val(pud)), addr,
> + PUD_SHIFT, next, flags, pages, nr))
> return 0;
> - } else if (!gup_pmd_range(pudp, pud, addr, next, flags, pages, nr))
> + } else if (!gup_fast_pmd_range(pudp, pud, addr, next, flags,
> + pages, nr))
> return 0;
> } while (pudp++, addr = next, addr != end);
>
> return 1;
> }
>
> -static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned long end,
> - unsigned int flags, struct page **pages, int *nr)
> +static int gup_fast_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
> + unsigned long end, unsigned int flags, struct page **pages,
> + int *nr)
> {
> unsigned long next;
> p4d_t *p4dp;
> @@ -3091,17 +3095,18 @@ static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned lo
> return 0;
> BUILD_BUG_ON(p4d_leaf(p4d));
> if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
> - if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
> - P4D_SHIFT, next, flags, pages, nr))
> + if (!gup_fast_hugepd(__hugepd(p4d_val(p4d)), addr,
> + P4D_SHIFT, next, flags, pages, nr))
> return 0;
> - } else if (!gup_pud_range(p4dp, p4d, addr, next, flags, pages, nr))
> + } else if (!gup_fast_pud_range(p4dp, p4d, addr, next, flags,
> + pages, nr))
> return 0;
> } while (p4dp++, addr = next, addr != end);
>
> return 1;
> }
>
> -static void gup_pgd_range(unsigned long addr, unsigned long end,
> +static void gup_fast_pgd_range(unsigned long addr, unsigned long end,
> unsigned int flags, struct page **pages, int *nr)
> {
> unsigned long next;
> @@ -3115,19 +3120,20 @@ static void gup_pgd_range(unsigned long addr, unsigned long end,
> if (pgd_none(pgd))
> return;
> if (unlikely(pgd_leaf(pgd))) {
> - if (!gup_huge_pgd(pgd, pgdp, addr, next, flags,
> - pages, nr))
> + if (!gup_fast_pgd_leaf(pgd, pgdp, addr, next, flags,
> + pages, nr))
> return;
> } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
> - if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
> - PGDIR_SHIFT, next, flags, pages, nr))
> + if (!gup_fast_hugepd(__hugepd(pgd_val(pgd)), addr,
> + PGDIR_SHIFT, next, flags, pages, nr))
> return;
> - } else if (!gup_p4d_range(pgdp, pgd, addr, next, flags, pages, nr))
> + } else if (!gup_fast_p4d_range(pgdp, pgd, addr, next, flags,
> + pages, nr))
> return;
> } while (pgdp++, addr = next, addr != end);
> }
> #else
> -static inline void gup_pgd_range(unsigned long addr, unsigned long end,
> +static inline void gup_fast_pgd_range(unsigned long addr, unsigned long end,
> unsigned int flags, struct page **pages, int *nr)
> {
> }
> @@ -3144,10 +3150,8 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
> }
> #endif
>
> -static unsigned long lockless_pages_from_mm(unsigned long start,
> - unsigned long end,
> - unsigned int gup_flags,
> - struct page **pages)
> +static unsigned long gup_fast(unsigned long start, unsigned long end,
> + unsigned int gup_flags, struct page **pages)
> {
> unsigned long flags;
> int nr_pinned = 0;
> @@ -3175,16 +3179,16 @@ static unsigned long lockless_pages_from_mm(unsigned long start,
> * that come from THPs splitting.
> */
> local_irq_save(flags);
> - gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
> + gup_fast_pgd_range(start, end, gup_flags, pages, &nr_pinned);
> local_irq_restore(flags);
>
> /*
> * When pinning pages for DMA there could be a concurrent write protect
> - * from fork() via copy_page_range(), in this case always fail fast GUP.
> + * from fork() via copy_page_range(), in this case always fail GUP-fast.
> */
> if (gup_flags & FOLL_PIN) {
> if (read_seqcount_retry(&current->mm->write_protect_seq, seq)) {
> - unpin_user_pages_lockless(pages, nr_pinned);
> + gup_fast_unpin_user_pages(pages, nr_pinned);
> return 0;
> } else {
> sanity_check_pinned_pages(pages, nr_pinned);
> @@ -3224,7 +3228,7 @@ static int internal_get_user_pages_fast(unsigned long start,
> if (unlikely(!access_ok((void __user *)start, len)))
> return -EFAULT;
>
> - nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages);
> + nr_pinned = gup_fast(start, end, gup_flags, pages);
> if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
> return nr_pinned;
>
> --
> 2.43.2
>

--
Sincerely yours,
Mike.