linux-kernel - Re: [PATCH v2 RESEND 1/2] arm64: avoid flushing icache multiple times on contiguous HugeTLB

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Message-ID: <Yh9julZqG+sr6IV9@arm.com>
Date:   Wed, 2 Mar 2022 12:31:54 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     will@...nel.org, akpm@...ux-foundation.org, david@...hat.com,
        bodeddub@...zon.com, osalvador@...e.de, mike.kravetz@...cle.com,
        rientjes@...gle.com, mark.rutland@....com, james.morse@....com,
        song.bao.hua@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        duanxiongchun@...edance.com, fam.zheng@...edance.com,
        smuchun@...il.com
Subject: Re: [PATCH v2 RESEND 1/2] arm64: avoid flushing icache multiple
 times on contiguous HugeTLB

On Wed, Mar 02, 2022 at 04:46:23PM +0800, Muchun Song wrote:
> When a contiguous HugeTLB page is mapped, set_pte_at() will be called
> CONT_PTES/CONT_PMDS times.  Therefore, __sync_icache_dcache() will
> flush cache multiple times if the page is executable (to ensure
> the I-D cache coherency).  However, the first flushing cache already
> covers subsequent cache flush operations.  So only flusing cache
> for the head page if it is a HugeTLB page to avoid redundant cache
> flushing.  In the next patch, it is also depends on this change
> since the tail vmemmap pages of HugeTLB is mapped with read-only
> meanning only head page struct can be modified.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>

(for this patch only, I have yet to figure out whether Anshuman's and
Mark's comments have been addressed in patch 2)

-- 
Catalin