Re: API for setting multiple PTEs at once

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Hi Matthew,

On 2/7/23 21:27, Matthew Wilcox wrote:
On Thu, Feb 02, 2023 at 09:14:23PM +0000, Matthew Wilcox wrote:
For those of you not subscribed, linux-mm is currently discussing
how best to handle page faults on large folios.  I simply made it work
when adding large folio support.  Now Yin Fengwei is working on
making it fast.
OK, here's an actual implementation:

It survives a run of xfstests.  If your architecture doesn't store its
PFNs at PAGE_SHIFT, you're going to want to implement your own set_ptes(),
or you'll see entirely the wrong pages mapped into userspace.  You may
also wish to implement set_ptes() if it can be done more efficiently
than __pte(pteval(pte) + PAGE_SIZE).

Architectures that implement things like flush_icache_page() and
update_mmu_cache() may want to propose batched versions of those.
That's alpha, csky, m68k, mips, nios2, parisc, sh,
arm, loongarch, openrisc, powerpc, riscv, sparc and xtensa.
Maintainers BCC'd, mailing lists CC'd.

I'm happy to collect implementations and submit them as part of a v6.

Please find below the riscv implementation for set_ptes:

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index ebee56d47003..10bf812776a4 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -463,6 +463,20 @@ static inline void set_pte_at(struct mm_struct *mm,
        __set_pte_at(mm, addr, ptep, pteval);

+#define set_ptes set_ptes
+static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
+                           pte_t *ptep, pte_t pte, unsigned int nr)
+       for (;;) {
+               set_pte_at(mm, addr, ptep, pte);
+               if (--nr == 0)
+                       break;
+               ptep++;
+               addr += PAGE_SIZE;
+               pte = __pte(pte_val(pte) + (1 << _PAGE_PFN_SHIFT));
+       }
 static inline void pte_clear(struct mm_struct *mm,
        unsigned long addr, pte_t *ptep)



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