linux-kernel - Re: [PATCH v2 1/3] mm: change huge_ptep_clear

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Message-ID: <Ynek+b3k6PVN3x7J@FVFYT0MHHV2J.usts.net>
Date:   Sun, 8 May 2022 19:09:45 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, mike.kravetz@...cle.com,
        catalin.marinas@....com, will@...nel.org,
        tsbogend@...ha.franken.de, James.Bottomley@...senPartnership.com,
        deller@....de, mpe@...erman.id.au, benh@...nel.crashing.org,
        paulus@...ba.org, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, ysato@...rs.sourceforge.jp, dalias@...c.org,
        davem@...emloft.net, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v2 1/3] mm: change huge_ptep_clear_flush() to return the
 original pte

On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
> It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
> table when unmapping or migrating a hugetlb page, and will change
> to use huge_ptep_clear_flush() instead in the following patches.
> 
> So this is a preparation patch, which changes the huge_ptep_clear_flush()
> to return the original pte to help to nuke a hugetlb page table.
> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Acked-by: Mike Kravetz <mike.kravetz@...cle.com>

Reviewed-by: Muchun Song <songmuchun@...edance.com>

But one nit below:

[...]
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8605d7e..61a21af 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>  		ClearHPageRestoreReserve(new_page);
>  
>  		/* Break COW or unshare */
> -		huge_ptep_clear_flush(vma, haddr, ptep);
> +		(void)huge_ptep_clear_flush(vma, haddr, ptep);

Why add a "(void)" here? Is there any warning if no "(void)"?
IIUC, I think we can remove this, right?

>  		mmu_notifier_invalidate_range(mm, range.start, range.end);
>  		page_remove_rmap(old_page, vma, true);
>  		hugepage_add_new_anon_rmap(new_page, vma, haddr);
> -- 
> 1.8.3.1
> 
>