linux-kernel - Re: [RFC PATCH 1/1] arm64: mm: remove unnecessary multiple tlb flush of contiguous hugetlb

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Message-ID: <Y+KWoDw1ppliQ5Sg@arm.com>
Date:   Tue, 7 Feb 2023 18:21:20 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Kaihao Bai <carlo.bai@...ux.alibaba.com>
Cc:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, anshuman.khandual@....com,
        baolin.wang@...ux.alibaba.com
Subject: Re: [RFC PATCH 1/1] arm64: mm: remove unnecessary multiple tlb flush
 of contiguous hugetlb

On Tue, Feb 07, 2023 at 07:09:41PM +0800, Kaihao Bai wrote:
> In arm64, contiguous flag refers to the same TLB entry that shared by a
> contiguous address range. If flush one entry of the address range, it
> would cover the whole contiguous address range. Thus there's no need to
> flush all contiguous range that CONT_PMD/PTE points to.

This doesn't work. The contiguous bit is a hint, so the CPU may not
coalesce multiple PTEs into a single TLB entry.

-- 
Catalin