Read-ahead code

Read-ahead code

[Luciano A. Stertz]

	I guess I found a bug in the readahead code, kernel 2.6.7.
	In filemap_nopage, if the memory area is not marked as sequential 
(VM_SEQ_READ isn't set) and the page is not in the page cache, the 
following code is executed:

1                ra_pages = max_sane_readahead(file->f_ra.ra_pages);
2                if (ra_pages) {
3                        long start;
4
5                        start = pgoff - ra_pages / 2;
6                        if (pgoff < 0)
7                                pgoff = 0;
8                        do_page_cache_readahead(mapping, file, pgoff, 
ra_pages);
9                }

	Seems that the author wanted to read ra_pages around pgoff. Shouldn't 
it be using 'start' instead of 'pgoff' in lines 6 to 8?!? Start is 
calculated and never used. Instead of reading pages from start to pgoff 
+ ra_pages/2, it's reading ra_pages from pgoff.

	Luciano

-- 
Luciano A. Stertz
luciano@tteng.com.br
T&T Engenheiros Associados Ltda
http://www.tteng.com.br-
Fone/Fax (51) 3224 8425
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Re: Read-ahead code

[Luciano A. Stertz]

	Oops, it's already fixed in 2.6.8-rc2, forget it.

	Luciano

Luciano A. Stertz wrote:
>     I guess I found a bug in the readahead code, kernel 2.6.7.
>     In filemap_nopage, if the memory area is not marked as sequential 
> (VM_SEQ_READ isn't set) and the page is not in the page cache, the 
> following code is executed:
> 
> 1                ra_pages = max_sane_readahead(file->f_ra.ra_pages);
> 2                if (ra_pages) {
> 3                        long start;
> 4
> 5                        start = pgoff - ra_pages / 2;
> 6                        if (pgoff < 0)
> 7                                pgoff = 0;
> 8                        do_page_cache_readahead(mapping, file, pgoff, 
> ra_pages);
> 9                }
> 
>     Seems that the author wanted to read ra_pages around pgoff. 
> Shouldn't it be using 'start' instead of 'pgoff' in lines 6 to 8?!? 
> Start is calculated and never used. Instead of reading pages from start 
> to pgoff + ra_pages/2, it's reading ra_pages from pgoff.
> 
>     Luciano
> 


-- 
Luciano A. Stertz
luciano@tteng.com.br
T&T Engenheiros Associados Ltda
http://www.tteng.com.br
Fone/Fax (51) 3224 8425
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"aart@kvack.org"> aart@kvack.org </a>