diff options
| -rw-r--r-- | include/linux/fs.h | 61 | ||||
| -rw-r--r-- | mm/readahead.c | 68 |
2 files changed, 31 insertions, 98 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h index 29cb32d..d33bead 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -695,16 +695,12 @@ struct fown_struct { /* * Track a single file's readahead state - * - * ================#============|==================#==================| - * ^ ^ ^ ^ - * file_ra_state.la_index .ra_index .lookahead_index .readahead_index */ struct file_ra_state { - pgoff_t la_index; /* enqueue time */ - pgoff_t ra_index; /* begin offset */ - pgoff_t lookahead_index; /* time to do next readahead */ - pgoff_t readahead_index; /* end offset */ + pgoff_t start; /* where readahead started */ + unsigned long size; /* # of readahead pages */ + unsigned long async_size; /* do asynchronous readahead when + there are only # of pages ahead */ unsigned long ra_pages; /* Maximum readahead window */ unsigned long mmap_hit; /* Cache hit stat for mmap accesses */ @@ -714,59 +710,14 @@ struct file_ra_state { }; /* - * Measuring read-ahead sizes. - * - * |----------- readahead size ------------>| - * ===#============|==================#=====================| - * |------- invoke interval ------>|-- lookahead size -->| - */ -static inline unsigned long ra_readahead_size(struct file_ra_state *ra) -{ - return ra->readahead_index - ra->ra_index; -} - -static inline unsigned long ra_lookahead_size(struct file_ra_state *ra) -{ - return ra->readahead_index - ra->lookahead_index; -} - -static inline unsigned long ra_invoke_interval(struct file_ra_state *ra) -{ - return ra->lookahead_index - ra->la_index; -} - -/* * Check if @index falls in the readahead windows. */ static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index) { - return (index >= ra->la_index && - index < ra->readahead_index); -} - -/* - * Where is the old read-ahead and look-ahead? - */ -static inline void ra_set_index(struct file_ra_state *ra, - pgoff_t la_index, pgoff_t ra_index) -{ - ra->la_index = la_index; - ra->ra_index = ra_index; + return (index >= ra->start && + index < ra->start + ra->size); } -/* - * Where is the new read-ahead and look-ahead? - */ -static inline void ra_set_size(struct file_ra_state *ra, - unsigned long ra_size, unsigned long la_size) -{ - ra->readahead_index = ra->ra_index + ra_size; - ra->lookahead_index = ra->ra_index + ra_size - la_size; -} - -unsigned long ra_submit(struct file_ra_state *ra, - struct address_space *mapping, struct file *filp); - struct file { /* * fu_list becomes invalid after file_free is called and queued via diff --git a/mm/readahead.c b/mm/readahead.c index 3d262bb..39bf45d 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); } |
