diff options
| -rw-r--r-- | mm/readahead.c | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index 8d6eeaaa6296..57557e294987 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -52,13 +52,24 @@ static inline unsigned long get_min_readahead(struct file_ra_state *ra) return (VM_MIN_READAHEAD * 1024) / PAGE_CACHE_SIZE; } +static inline void reset_ahead_window(struct file_ra_state *ra) +{ + /* + * ... but preserve ahead_start + ahead_size value, + * see 'recheck:' label in page_cache_readahead(). + * Note: We never use ->ahead_size as rvalue without + * checking ->ahead_start != 0 first. + */ + ra->ahead_size += ra->ahead_start; + ra->ahead_start = 0; +} + static inline void ra_off(struct file_ra_state *ra) { ra->start = 0; ra->flags = 0; ra->size = 0; - ra->ahead_start = 0; - ra->ahead_size = 0; + reset_ahead_window(ra); return; } @@ -426,8 +437,7 @@ static int make_ahead_window(struct address_space *mapping, struct file *filp, * congestion. The ahead window will any way be closed * in case we failed due to excessive page cache hits. */ - ra->ahead_start = 0; - ra->ahead_size = 0; + reset_ahead_window(ra); } return ret; @@ -520,11 +530,11 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, * If we get here we are doing sequential IO and this was not the first * occurence (ie we have an existing window) */ - if (ra->ahead_start == 0) { /* no ahead window yet */ if (!make_ahead_window(mapping, filp, ra, 0)) - goto out; + goto recheck; } + /* * Already have an ahead window, check if we crossed into it. * If so, shift windows and issue a new ahead window. @@ -536,6 +546,10 @@ page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra, ra->start = ra->ahead_start; ra->size = ra->ahead_size; make_ahead_window(mapping, filp, ra, 0); +recheck: + /* prev_page shouldn't overrun the ahead window */ + ra->prev_page = min(ra->prev_page, + ra->ahead_start + ra->ahead_size - 1); } out: |