Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in find_vma()

From	Chen Gang <xili_gchen_5257@hotmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in find_vma()
Date	2015-09-11 00:20 +0200
Message-ID	<q7ime-6uu-11@gated-at.bofh.it> (permalink)
References	<q5mki-2Hy-11@gated-at.bofh.it> <q6rUB-6Ec-15@gated-at.bofh.it> <q6WlI-8l1-13@gated-at.bofh.it> <q7eLE-11U-23@gated-at.bofh.it>
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On 9/11/15 02:19, Oleg Nesterov wrote:
> On 09/10, Chen Gang wrote:
>> - If "addr>= vm_start", we return this vma (else continue searching).
> 
> This is optimization, we can stop the search because in this case
> vma == tmp is obviously the 1st vma with "addr < vm_end".
> 

OK, thanks.

I guess if we have additional comments for "if (tmp->vm_start <= addr)",
the code will be more readable for readers (especially for newbies).

@@ -2064,7 +2064,7 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
                if (tmp->vm_end > addr) {
                        vma = tmp;
                        if (tmp->vm_start <= addr)
-                               break;
+                               break; /* It must be 1st "addr < vm_end" */
                        rb_node = rb_node->rb_left;
                } else
                        rb_node = rb_node->rb_right;


> I simply can't understand your concerns. Perhaps you can make a
> patch, then it will be more clear what me-or-you have missed.
> 

I guess, we need not (it is my missing). :-)


Thanks.
-- 
Chen Gang (陈刚)

Open, share, and attitude like air, water, and life which God blessed
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Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in  find_vma() Chen Gang <xili_gchen_5257@hotmail.com> - 2015-09-08 16:20 +0200
  Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in  find_vma() Oleg Nesterov <oleg@redhat.com> - 2015-09-09 18:30 +0200
  Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in  find_vma() Chen Gang <xili_gchen_5257@hotmail.com> - 2015-09-10 00:50 +0200
    Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in  find_vma() Oleg Nesterov <oleg@redhat.com> - 2015-09-10 20:30 +0200
      Re: [PATCH] mm/mmap.c: Remove useless statement "vma = NULL" in find_vma() Chen Gang <xili_gchen_5257@hotmail.com> - 2015-09-11 00:20 +0200

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