From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH 2/4] mm: speed up mremap by 500x on large regions (v2)
Date: Wed, 24 Oct 2018 13:12:56 +0300
Message-ID: <20181024101255.it4lptrjogalxbey@kshutemo-mobl1>
References: <20181013013200.206928-1-joel@joelfernandes.org>
 <20181013013200.206928-3-joel@joelfernandes.org>
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Cc: linux-mips@linux-mips.org, Rich Felker <dalias@libc.org>,
 linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
 Peter Zijlstra <peterz@infradead.org>,
 Catalin Marinas <catalin.marinas@arm.com>,
 Dave Hansen <dave.hansen@linux.intel.com>, Will Deacon <will.deacon@arm.com>,
 mhocko@kernel.org, linux-mm@kvack.org, lokeshgidra@google.com,
 sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org,
 elfring@users.sourceforge.net, Jonas Bonn <jonas@southpole.se>,
 kvmarm@lists.cs.columbia.edu, dancol@google.com,
 Yoshinori Sato <ysato@users.sourceforge.jp>, linux-xtensa@linux-xtensa.org,
 linux-hexagon@vger.kernel.org, Helge Deller <deller@gmx.de>,
 "maintainer:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" <x86@kernel.org>,
 hughd@google.com, "James E.J. Bottomley" <jejb@parisc-linux.org>,
 kasan-dev@googlegroups.com, anton.ivanov@kot-begemot.co.uk,
 Ingo Molnar <mingo@redhat.com>, Geert Uy
To: "Joel Fernandes (Google)" <joel@joelfernandes.org>
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Errors-To: linux-snps-arc-bounces+gla-linux-snps-arc=m.gmane.org@lists.infradead.org

On Fri, Oct 12, 2018 at 06:31:58PM -0700, Joel Fernandes (Google) wrote:
> diff --git a/mm/mremap.c b/mm/mremap.c
> index 9e68a02a52b1..2fd163cff406 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -191,6 +191,54 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
>  		drop_rmap_locks(vma);
>  }
>  
> +static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
> +		  unsigned long new_addr, unsigned long old_end,
> +		  pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
> +{
> +	spinlock_t *old_ptl, *new_ptl;
> +	struct mm_struct *mm = vma->vm_mm;
> +
> +	if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK)
> +	    || old_end - old_addr < PMD_SIZE)
> +		return false;
> +
> +	/*
> +	 * The destination pmd shouldn't be established, free_pgtables()
> +	 * should have release it.
> +	 */
> +	if (WARN_ON(!pmd_none(*new_pmd)))
> +		return false;
> +
> +	/*
> +	 * We don't have to worry about the ordering of src and dst
> +	 * ptlocks because exclusive mmap_sem prevents deadlock.
> +	 */
> +	old_ptl = pmd_lock(vma->vm_mm, old_pmd);
> +	if (old_ptl) {

How can it ever be false?

> +		pmd_t pmd;
> +
> +		new_ptl = pmd_lockptr(mm, new_pmd);
> +		if (new_ptl != old_ptl)
> +			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
> +
> +		/* Clear the pmd */
> +		pmd = *old_pmd;
> +		pmd_clear(old_pmd);
> +
> +		VM_BUG_ON(!pmd_none(*new_pmd));
> +
> +		/* Set the new pmd */
> +		set_pmd_at(mm, new_addr, new_pmd, pmd);
> +		if (new_ptl != old_ptl)
> +			spin_unlock(new_ptl);
> +		spin_unlock(old_ptl);
> +
> +		*need_flush = true;
> +		return true;
> +	}
> +	return false;
> +}
> +
-- 
 Kirill A. Shutemov