diff options
Diffstat (limited to 'mm/readahead.c')
| -rw-r--r-- | mm/readahead.c | 68 |
1 files changed, 25 insertions, 43 deletions
diff --git a/mm/readahead.c b/mm/readahead.c index 3d262bb738a..39bf45d4332 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -253,21 +253,16 @@ unsigned long max_sane_readahead(unsigned long nr) /* * Submit IO for the read-ahead request in file_ra_state. */ -unsigned long ra_submit(struct file_ra_state *ra, +static unsigned long ra_submit(struct file_ra_state *ra, struct address_space *mapping, struct file *filp) { - unsigned long ra_size; - unsigned long la_size; int actual; - ra_size = ra_readahead_size(ra); - la_size = ra_lookahead_size(ra); actual = __do_page_cache_readahead(mapping, filp, - ra->ra_index, ra_size, la_size); + ra->start, ra->size, ra->async_size); return actual; } -EXPORT_SYMBOL_GPL(ra_submit); /* * Set the initial window size, round to next power of 2 and square @@ -296,7 +291,7 @@ static unsigned long get_init_ra_size(unsigned long size, unsigned long max) static unsigned long get_next_ra_size(struct file_ra_state *ra, unsigned long max) { - unsigned long cur = ra->readahead_index - ra->ra_index; + unsigned long cur = ra->size; unsigned long newsize; if (cur < max / 16) @@ -313,28 +308,21 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra, * The fields in struct file_ra_state represent the most-recently-executed * readahead attempt: * - * |-------- last readahead window -------->| - * |-- application walking here -->| - * ======#============|==================#=====================| - * ^la_index ^ra_index ^lookahead_index ^readahead_index - * - * [ra_index, readahead_index) represents the last readahead window. - * - * [la_index, lookahead_index] is where the application would be walking(in - * the common case of cache-cold sequential reads): the last window was - * established when the application was at la_index, and the next window will - * be bring in when the application reaches lookahead_index. + * |<----- async_size ---------| + * |------------------- size -------------------->| + * |==================#===========================| + * ^start ^page marked with PG_readahead * * To overlap application thinking time and disk I/O time, we do * `readahead pipelining': Do not wait until the application consumed all * readahead pages and stalled on the missing page at readahead_index; - * Instead, submit an asynchronous readahead I/O as early as the application - * reads on the page at lookahead_index. Normally lookahead_index will be - * equal to ra_index, for maximum pipelining. + * Instead, submit an asynchronous readahead I/O as soon as there are + * only async_size pages left in the readahead window. Normally async_size + * will be equal to size, for maximum pipelining. * * In interleaved sequential reads, concurrent streams on the same fd can * be invalidating each other's readahead state. So we flag the new readahead - * page at lookahead_index with PG_readahead, and use it as readahead + * page at (start+size-async_size) with PG_readahead, and use it as readahead * indicator. The flag won't be set on already cached pages, to avoid the * readahead-for-nothing fuss, saving pointless page cache lookups. * @@ -363,24 +351,21 @@ ondemand_readahead(struct address_space *mapping, unsigned long req_size) { unsigned long max; /* max readahead pages */ - pgoff_t ra_index; /* readahead index */ - unsigned long ra_size; /* readahead size */ - unsigned long la_size; /* lookahead size */ int sequential; max = ra->ra_pages; sequential = (offset - ra->prev_index <= 1UL) || (req_size > max); /* - * Lookahead/readahead hit, assume sequential access. + * It's the expected callback offset, assume sequential access. * Ramp up sizes, and push forward the readahead window. */ - if (offset && (offset == ra->lookahead_index || - offset == ra->readahead_index)) { - ra_index = ra->readahead_index; - ra_size = get_next_ra_size(ra, max); - la_size = ra_size; - goto fill_ra; + if (offset && (offset == (ra->start + ra->size - ra->async_size) || + offset == (ra->start + ra->size))) { + ra->start += ra->size; + ra->size = get_next_ra_size(ra, max); + ra->async_size = ra->size; + goto readit; } /* @@ -399,24 +384,21 @@ ondemand_readahead(struct address_space *mapping, * - oversize random read * Start readahead for it. */ - ra_index = offset; - ra_size = get_init_ra_size(req_size, max); - la_size = ra_size > req_size ? ra_size - req_size : ra_size; + ra->start = offset; + ra->size = get_init_ra_size(req_size, max); + ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size; /* - * Hit on a lookahead page without valid readahead state. + * Hit on a marked page without valid readahead state. * E.g. interleaved reads. * Not knowing its readahead pos/size, bet on the minimal possible one. */ if (hit_readahead_marker) { - ra_index++; - ra_size = min(4 * ra_size, max); + ra->start++; + ra->size = get_next_ra_size(ra, max); } -fill_ra: - ra_set_index(ra, offset, ra_index); - ra_set_size(ra, ra_size, la_size); - +readit: return ra_submit(ra, mapping, filp); } |