unused 'size' assignment in filemap_nopage

unused 'size' assignment in filemap_nopage

[Jeff Moyer]

filemap_nopage has the following code:

retry_all:
	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
	if (pgoff >= size)
		goto outside_data_content;

	/* If we don't want any read-ahead, don't bother */
	if (VM_RandomReadHint(area))
		goto no_cached_page;

	/*
	 * The "size" of the file, as far as mmap is concerned, isn't bigger
	 * than the mapping
	 */
	if (size > endoff)
		size = endoff;


After this, size is not referenced.  So, either this potential reassignment
of size is superfluous, or we are missing some other code later on in the
function.  If it is the former, I've attached a patch which will remove the
code.

Thanks,

Jeff

--- linux-2.6.12-rc1/mm/filemap.c.orig	2005-03-22 16:28:01.429426880 -0500
+++ linux-2.6.12-rc1/mm/filemap.c	2005-03-22 16:29:22.564092536 -0500
@@ -1191,13 +1191,6 @@ retry_all:
 		goto no_cached_page;
 
 	/*
-	 * The "size" of the file, as far as mmap is concerned, isn't bigger
-	 * than the mapping
-	 */
-	if (size > endoff)
-		size = endoff;
-
-	/*
 	 * The readahead code wants to be told about each and every page
 	 * so it can build and shrink its windows appropriately
 	 *

Re: unused 'size' assignment in filemap_nopage

[Jan Engelhardt]

>	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
>	if (pgoff >= size)
>		goto outside_data_content;
>	...
>	if (size > endoff)
>		size = endoff;
>
>After this, size is not referenced.  So, either this potential reassignment
>of size is superfluous, or we are missing some other code later on in the
>function.  If it is the former, I've attached a patch which will remove the
>code.

Only if you can make sure the SIZE will never be bigger than ENDOFF.
What you see here is basically:
  size = min(endoff, (i_size_read...))
With a pgoff>=size somewhere ;)


Jan Engelhardt
-- 

Re: unused 'size' assignment in filemap_nopage

[Herbert Xu]

Jeff Moyer <jmoyer@redhat.com> wrote:
> 
> After this, size is not referenced.  So, either this potential reassignment
> of size is superfluous, or we are missing some other code later on in the
> function.  If it is the former, I've attached a patch which will remove the
> code.

Yes it's obsolete.  You can remove endoff as well.
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
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Re: unused 'size' assignment in filemap_nopage

[Jeff Moyer]

==> Regarding Re: unused 'size' assignment in filemap_nopage; Herbert Xu <herbert@gondor.apana.org.au> adds:

herbert> Jeff Moyer <jmoyer@redhat.com> wrote:
>> After this, size is not referenced.  So, either this potential
>> reassignment of size is superfluous, or we are missing some other code
>> later on in the function.  If it is the former, I've attached a patch
>> which will remove the code.

herbert> Yes it's obsolete.  You can remove endoff as well.

Okay, here's the patch.

Thanks,

Jeff

--- linux-2.6.11/mm/filemap.c.orig	2005-03-23 08:32:38.182822976 -0500
+++ linux-2.6.11/mm/filemap.c	2005-03-23 08:33:34.966190592 -0500
@@ -1175,11 +1175,10 @@ struct page * filemap_nopage(struct vm_a
 	struct file_ra_state *ra = &file->f_ra;
 	struct inode *inode = mapping->host;
 	struct page *page;
-	unsigned long size, pgoff, endoff;
+	unsigned long size, pgoff;
 	int did_readaround = 0, majmin = VM_FAULT_MINOR;
 
 	pgoff = ((address - area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;
-	endoff = ((area->vm_end - area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;
 
 retry_all:
 	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
@@ -1191,13 +1190,6 @@ retry_all:
 		goto no_cached_page;
 
 	/*
-	 * The "size" of the file, as far as mmap is concerned, isn't bigger
-	 * than the mapping
-	 */
-	if (size > endoff)
-		size = endoff;
-
-	/*
 	 * The readahead code wants to be told about each and every page
 	 * so it can build and shrink its windows appropriately
 	 *