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SubjectRe: [PATCH 3/4] cleanup ahead window calculation
Not sure how much better this is, but it doesn't hurt anything.

Steve

Oleg Nesterov wrote:

>This patch moves some code into the get_next_ra_size()
>and renames it into 'set_next_ahead_window'.
>
>Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
>
>--- 2.6.11-rc2/mm/readahead.c~ 2005-01-25 15:17:13.000000000 +0300
>+++ 2.6.11-rc2/mm/readahead.c 2005-01-25 16:51:50.000000000 +0300
>@@ -85,20 +85,23 @@ static unsigned long get_init_ra_size(un
> * not for each call to readahead. If a cache miss occured, reduce next I/O
> * size, else increase depending on how close to max we are.
> */
>-static unsigned long get_next_ra_size(unsigned long cur, unsigned long max,
>- unsigned long min, unsigned long * flags)
>+static void set_next_ahead_window(struct file_ra_state *ra,
>+ unsigned long max, unsigned long min)
> {
> unsigned long newsize;
>+ unsigned long cur = ra->size;
>
>- if (*flags & RA_FLAG_MISS) {
>+ ra->ahead_start = ra->start + cur;
>+
>+ if (ra->flags & RA_FLAG_MISS) {
>+ ra->flags &= ~RA_FLAG_MISS;
> newsize = max((cur - 2), min);
>- *flags &= ~RA_FLAG_MISS;
>- } else if (cur < max / 16) {
>+ } else if (cur < max / 16)
> newsize = 4 * cur;
>- } else {
>+ else
> newsize = 2 * cur;
>- }
>- return min(newsize, max);
>+
>+ ra->ahead_size = min(newsize, max);
> }
>
> #define list_to_page(head) (list_entry((head)->prev, struct page, lru))
>@@ -457,9 +460,7 @@ page_cache_readahead(struct address_spac
> * immediately.
> */
> if (req_size >= max) {
>- ra->ahead_size = get_next_ra_size(ra->size, max, min,
>- &ra->flags);
>- ra->ahead_start = ra->start + ra->size;
>+ set_next_ahead_window(ra, max, min);
> blockable_page_cache_readahead(mapping, filp,
> ra->ahead_start, ra->ahead_size, ra, 1);
> }
>@@ -497,9 +498,7 @@ page_cache_readahead(struct address_spac
> ra->size = ra->ahead_size;
> }
>
>- ra->ahead_size = get_next_ra_size(ra->size, max, min,
>- &ra->flags);
>- ra->ahead_start = ra->start + ra->size;
>+ set_next_ahead_window(ra, max, min);
>
> block = ((offset + newsize - 1) >= ra->ahead_start);
> if (!blockable_page_cache_readahead(mapping, filp,
>
>

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