linux-kernel - Re: [RFC 13/20] mm/tlb: introduce tlb_start_ptes() and tlb_end

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Message-ID: <YBf/1H/zZ2LNDf3U@hirez.programming.kicks-ass.net>
Date:   Mon, 1 Feb 2021 14:19:16 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Nadav Amit <namit@...are.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Nick Piggin <npiggin@...il.com>, x86@...nel.org
Subject: Re: [RFC 13/20] mm/tlb: introduce tlb_start_ptes() and tlb_end_ptes()

On Sat, Jan 30, 2021 at 04:11:25PM -0800, Nadav Amit wrote:
> +#define tlb_start_ptes(tlb)						\
> +	do {								\
> +		struct mmu_gather *_tlb = (tlb);			\
> +									\
> +		flush_tlb_batched_pending(_tlb->mm);			\
> +	} while (0)
> +
> +static inline void tlb_end_ptes(struct mmu_gather *tlb) { }

>  	tlb_change_page_size(tlb, PAGE_SIZE);
>  	orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> -	flush_tlb_batched_pending(mm);
> +	tlb_start_ptes(tlb);
>  	arch_enter_lazy_mmu_mode();
>  	for (; addr < end; pte++, addr += PAGE_SIZE) {
>  		ptent = *pte;
> @@ -468,6 +468,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
>  	}
>  
>  	arch_leave_lazy_mmu_mode();
> +	tlb_end_ptes(tlb);
>  	pte_unmap_unlock(orig_pte, ptl);
>  	if (pageout)
>  		reclaim_pages(&page_list);

I don't like how you're dubbling up on arch_*_lazy_mmu_mode(). It seems
to me those should be folded into tlb_{start,end}_ptes().

Alternatively, the even more work approach would be to, add an optional
@tlb argument to pte_offset_map_lock()/pte_unmap_unlock() and friends.