/*
* 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
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)
* 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.
*
static unsigned long
ondemand_readahead(struct address_space *mapping,
struct file_ra_state *ra, struct file *filp,
- struct page *page, pgoff_t offset,
+ bool hit_readahead_marker, pgoff_t offset,
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;
}
/*
* Standalone, small read.
* Read as is, and do not pollute the readahead state.
*/
- if (!page && !sequential) {
+ if (!hit_readahead_marker && !sequential) {
return __do_page_cache_readahead(mapping, filp,
offset, req_size, 0);
}
* - 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 (page) {
- ra_index++;
- ra_size = min(4 * ra_size, max);
+ if (hit_readahead_marker) {
+ 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);
}
/**
- * page_cache_readahead_ondemand - generic file readahead
+ * page_cache_sync_readahead - generic file readahead
* @mapping: address_space which holds the pagecache and I/O vectors
* @ra: file_ra_state which holds the readahead state
* @filp: passed on to ->readpage() and ->readpages()
- * @page: the page at @offset, or NULL if non-present
- * @offset: start offset into @mapping, in PAGE_CACHE_SIZE units
+ * @offset: start offset into @mapping, in pagecache page-sized units
* @req_size: hint: total size of the read which the caller is performing in
- * PAGE_CACHE_SIZE units
+ * pagecache pages
*
- * page_cache_readahead_ondemand() is the entry point of readahead logic.
- * This function should be called when it is time to perform readahead:
- * 1) @page == NULL
- * A cache miss happened, time for synchronous readahead.
- * 2) @page != NULL && PageReadahead(@page)
- * A look-ahead hit occured, time for asynchronous readahead.
+ * page_cache_sync_readahead() should be called when a cache miss happened:
+ * it will submit the read. The readahead logic may decide to piggyback more
+ * pages onto the read request if access patterns suggest it will improve
+ * performance.
*/
-unsigned long
-page_cache_readahead_ondemand(struct address_space *mapping,
- struct file_ra_state *ra, struct file *filp,
- struct page *page, pgoff_t offset,
- unsigned long req_size)
+void page_cache_sync_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ pgoff_t offset, unsigned long req_size)
{
/* no read-ahead */
if (!ra->ra_pages)
- return 0;
-
- if (page) {
- /*
- * It can be PG_reclaim.
- */
- if (PageWriteback(page))
- return 0;
-
- ClearPageReadahead(page);
-
- /*
- * Defer asynchronous read-ahead on IO congestion.
- */
- if (bdi_read_congested(mapping->backing_dev_info))
- return 0;
- }
+ return;
+
+ /* do read-ahead */
+ ondemand_readahead(mapping, ra, filp, false, offset, req_size);
+}
+EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
+
+/**
+ * page_cache_async_readahead - file readahead for marked pages
+ * @mapping: address_space which holds the pagecache and I/O vectors
+ * @ra: file_ra_state which holds the readahead state
+ * @filp: passed on to ->readpage() and ->readpages()
+ * @page: the page at @offset which has the PG_readahead flag set
+ * @offset: start offset into @mapping, in pagecache page-sized units
+ * @req_size: hint: total size of the read which the caller is performing in
+ * pagecache pages
+ *
+ * page_cache_async_ondemand() should be called when a page is used which
+ * has the PG_readahead flag: this is a marker to suggest that the application
+ * has used up enough of the readahead window that we should start pulling in
+ * more pages. */
+void
+page_cache_async_readahead(struct address_space *mapping,
+ struct file_ra_state *ra, struct file *filp,
+ struct page *page, pgoff_t offset,
+ unsigned long req_size)
+{
+ /* no read-ahead */
+ if (!ra->ra_pages)
+ return;
+
+ /*
+ * Same bit is used for PG_readahead and PG_reclaim.
+ */
+ if (PageWriteback(page))
+ return;
+
+ ClearPageReadahead(page);
+
+ /*
+ * Defer asynchronous read-ahead on IO congestion.
+ */
+ if (bdi_read_congested(mapping->backing_dev_info))
+ return;
/* do read-ahead */
- return ondemand_readahead(mapping, ra, filp, page,
- offset, req_size);
+ ondemand_readahead(mapping, ra, filp, true, offset, req_size);
}
-EXPORT_SYMBOL_GPL(page_cache_readahead_ondemand);
+EXPORT_SYMBOL_GPL(page_cache_async_readahead);
git.openpandora.org / pandora-kernel.git / blobdiff