linux-kernel - Re: [PATCH v3 21/34] s390: Implement the new page table range API

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Message-ID: <20230302143154.1886c213@thinkpad-T15>
Date:   Thu, 2 Mar 2023 14:31:54 +0100
From:   Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 21/34] s390: Implement the new page table range API

On Tue, 28 Feb 2023 21:37:24 +0000
"Matthew Wilcox (Oracle)" <willy@...radead.org> wrote:

> Add set_ptes() and update_mmu_cache_range().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
> Cc: Sven Schnelle <svens@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> ---
>  arch/s390/include/asm/pgtable.h | 34 ++++++++++++++++++++++++---------
>  1 file changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 2c70b4d1263d..46bf475116f1 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -50,6 +50,7 @@ void arch_report_meminfo(struct seq_file *m);
>   * tables contain all the necessary information.
>   */
>  #define update_mmu_cache(vma, address, ptep)     do { } while (0)
> +#define update_mmu_cache_range(vma, addr, ptep, nr)	do { } while (0)
>  #define update_mmu_cache_pmd(vma, address, ptep) do { } while (0)
>  
>  /*
> @@ -1317,21 +1318,36 @@ pgprot_t pgprot_writecombine(pgprot_t prot);
>  pgprot_t pgprot_writethrough(pgprot_t prot);
>  
>  /*
> - * Certain architectures need to do special things when PTEs
> - * within a page table are directly modified.  Thus, the following
> - * hook is made available.
> + * Set multiple PTEs to consecutive pages with a single call.  All PTEs
> + * are within the same folio, PMD and VMA.
>   */
> -static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> -			      pte_t *ptep, pte_t entry)
> +static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
> +			      pte_t *ptep, pte_t entry, unsigned int nr)
>  {
>  	if (pte_present(entry))
>  		entry = clear_pte_bit(entry, __pgprot(_PAGE_UNUSED));
> -	if (mm_has_pgste(mm))
> -		ptep_set_pte_at(mm, addr, ptep, entry);
> -	else
> -		set_pte(ptep, entry);
> +	if (mm_has_pgste(mm)) {
> +		for (;;) {
> +			ptep_set_pte_at(mm, addr, ptep, entry);

There might be room for additional optimization here, regarding the
preempt_disable/enable() in ptep_set_pte_at(), i.e. move it out of
ptep_set_pte_at() and do it only once in this loop.

We could add that later with an add-on patch, but for this series it
all looks good.

Reviewed-by: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>