Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:2 as permitted sender) client-ip=2620:137:e000::3:2;
From:   Barry Song <21cnbao@gmail.com>
To:     ryan.roberts@arm.com
Cc:     akpm@linux-foundation.org, andreyknvl@gmail.com,
        anshuman.khandual@arm.com, ardb@kernel.org,
        catalin.marinas@arm.com, david@redhat.com, dvyukov@google.com,
        glider@google.com, james.morse@arm.com, jhubbard@nvidia.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, mark.rutland@arm.com, maz@kernel.org,
        oliver.upton@linux.dev, ryabinin.a.a@gmail.com,
        suzuki.poulose@arm.com, vincenzo.frascino@arm.com,
        wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org,
        yuzenghui@huawei.com, yuzhao@google.com, ziy@nvidia.com
Subject: Re: [PATCH v2 14/14] arm64/mm: Add ptep_get_and_clear_full() to optimize process teardown
Date:   Tue, 28 Nov 2023 20:32:54 +1300
Message-Id: <20231128073254.37870-1-v-songbaohua@oppo.com>
In-Reply-To: <20231115163018.1303287-15-ryan.roberts@arm.com>
References: <20231115163018.1303287-15-ryan.roberts@arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

> +#define __HAVE_ARCH_PTEP_GET_AND_CLEAR_FULL
> +static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
> +				unsigned long addr, pte_t *ptep, int full)
> +{
> +	pte_t orig_pte = __ptep_get(ptep);
> +
> +	if (!pte_valid_cont(orig_pte) || !full) {
> +		contpte_try_unfold(mm, addr, ptep, orig_pte);
> +		return __ptep_get_and_clear(mm, addr, ptep);
> +	} else
> +		return contpte_ptep_get_and_clear_full(mm, addr, ptep);
> +}
> +

Hi Ryan,

I feel quite hard to understand the code. when !pte_valid_cont(orig_pte),
we will call contpte_try_unfold(mm, addr, ptep, orig_pte);

but in contpte_try_unfold(), we call unfold only if pte_valid_cont()
is true:
static inline void contpte_try_unfold(struct mm_struct *mm, unsigned long addr,
                                        pte_t *ptep, pte_t pte) 
{
        if (contpte_is_enabled(mm) && pte_valid_cont(pte))
                __contpte_try_unfold(mm, addr, ptep, pte);
}

so do you mean the below?

if (!pte_valid_cont(orig_pte))
	return __ptep_get_and_clear(mm, addr, ptep);

if (!full) {
	contpte_try_unfold(mm, addr, ptep, orig_pte);
	return __ptep_get_and_clear(mm, addr, ptep);	
} else {
	return contpte_ptep_get_and_clear_full(mm, addr, ptep);
}

Thanks
Barry