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mm/readahead: simplify page_cache_ra_unbounded loop counter reset

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Minor cleanup, no behavior change intended.

`read_pages` ensures that `ractl->_nr_pages` is zero before it returns, so
the `ractl->_nr_pages` term in these expressions contributes nothing. 
This seems to have been true since the statements were introduced in
commit f615bd5c47 ("mm/readahead: Handle ractl nr_pages being
modified").

The new expression has an intuitive explanation.  When filesystems perform
readahead, they increment `ractl->_index` by the number of pages
processed, so, after `read_pages` returns, `ractl->_index` points to the
first page after those already processed.  `index` points to the first
page considered in the loop.  So, `ractl->_index - index` is the number of
pages processed by the loop so far.

Link: https://lore.kernel.org/20260512203154.754075-3-fmayle@google.com
Signed-off-by: Frederick Mayle <fmayle@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Frederick Mayle 2026-05-12 13:31:36 -07:00 committed by Andrew Morton
parent c516c365d9
commit 418bffb6ba
1 changed files with 2 additions and 2 deletions
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4
mm/readahead.c
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@ -281,7 +281,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
*/
read_pages(ractl);
ractl->_index += min_nrpages;
i = ractl->_index + ractl->_nr_pages - index;
i = ractl->_index - index;
continue;
}
@ -297,7 +297,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
break;
read_pages(ractl);
ractl->_index += min_nrpages;
i = ractl->_index + ractl->_nr_pages - index;
i = ractl->_index - index;
continue;
}
if (i == mark)