linux-kernel - Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in find

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Date:	Wed, 9 Sep 2015 18:26:05 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Chen Gang <xili_gchen_5257@...mail.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"riel@...hat.com" <riel@...hat.com>, Michal Hocko <mhocko@...e.cz>,
	"sasha.levin@...cle.com" <sasha.levin@...cle.com>,
	"pfeiner@...gle.com" <pfeiner@...gle.com>,
	"aarcange@...hat.com" <aarcange@...hat.com>,
	"vishnu.ps@...sung.com" <vishnu.ps@...sung.com>,
	Linux Memory <linux-mm@...ck.org>,
	kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in
	find_vma()

On 09/08, Chen Gang wrote:
>
> I also want to consult: the comments of find_vma() says:

Sorry, I don't understand the question ;)

> "Look up the first VMA which satisfies addr < vm_end, ..."
>
> Is it OK?

Why not?

> (why not "vm_start <= addr < vm_end"),

Because this some callers actually want to find the 1st vma which
satisfies addr < vm_end? For example, shift_arg_pages().

OTOH, I think that another helper,

	find_vma_xxx(mm, addr)
	{
		vma = find_vma(...)
		if (vma && vma->vm_start > addr)
			vma = NULL;
		return vma;
	}

makes sense. It can have a lot of users.

> need we let "vma = tmp"
> in "if (tmp->vm_start <= addr)"? -- it looks the comments is not match
> the implementation, precisely (maybe not 1st VMA).

This contradicts with above... I mean, it is not clear what exactly do
you blame, semantics or implementation.

The implementation looks correct. Why do you think it can be not 1st vma?

Oleg.

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