Read-ahead code

"Luciano A. Stertz" <luciano@xxxxxxxxxxxx> · Tue, 27 Jul 2004 10:29:26 -0300



	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@xxxxxxxxxxxx
T&T Engenheiros Associados Ltda
http://www.tteng.com.br-
Fone/Fax (51) 3224 8425


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