1 files changed, 483 insertions, 0 deletions
diff --git a/mm/readahead.c b/mm/readahead.c
new file mode 100644
index 0000000..bec83c1
--- /dev/null
+++ b/mm/readahead.c
@@ -0,0 +1,483 @@
+/*
+ * mm/readahead.c - address_space-level file readahead.
+ *
+ * Copyright (C) 2002, Linus Torvalds
+ *
+ * 09Apr2002	Andrew Morton
+ *		Initial version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/blkdev.h>
+#include <linux/backing-dev.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/pagevec.h>
+#include <linux/pagemap.h>
+
+void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
+{
+}
+EXPORT_SYMBOL(default_unplug_io_fn);
+
+struct backing_dev_info default_backing_dev_info = {
+	.ra_pages	= VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE,
+	.state		= 0,
+	.capabilities	= BDI_CAP_MAP_COPY,
+	.unplug_io_fn	= default_unplug_io_fn,
+};
+EXPORT_SYMBOL_GPL(default_backing_dev_info);
+
+/*
+ * Initialise a struct file's readahead state.  Assumes that the caller has
+ * memset *ra to zero.
+ */
+void
+file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
+{
+	ra->ra_pages = mapping->backing_dev_info->ra_pages;
+	ra->prev_pos = -1;
+}
+EXPORT_SYMBOL_GPL(file_ra_state_init);
+
+#define list_to_page(head) (list_entry((head)->prev, struct page, lru))
+
+/**
+ * read_cache_pages - populate an address space with some pages & start reads against them
+ * @mapping: the address_space
+ * @pages: The address of a list_head which contains the target pages.  These
+ *   pages have their ->index populated and are otherwise uninitialised.
+ * @filler: callback routine for filling a single page.
+ * @data: private data for the callback routine.
+ *
+ * Hides the details of the LRU cache etc from the filesystems.
+ */
+int read_cache_pages(struct address_space *mapping, struct list_head *pages,
+			int (*filler)(void *, struct page *), void *data)
+{
+	struct page *page;
+	int ret = 0;
+
+	while (!list_empty(pages)) {
+		page = list_to_page(pages);
+		list_del(&page->lru);
+		if (add_to_page_cache_lru(page, mapping,
+					page->index, GFP_KERNEL)) {
+			page_cache_release(page);
+			continue;
+		}
+		page_cache_release(page);
+
+		ret = filler(data, page);
+		if (unlikely(ret)) {
+			put_pages_list(pages);
+			break;
+		}
+		task_io_account_read(PAGE_CACHE_SIZE);
+	}
+	return ret;
+}
+
+EXPORT_SYMBOL(read_cache_pages);
+
+static int read_pages(struct address_space *mapping, struct file *filp,
+		struct list_head *pages, unsigned nr_pages)
+{
+	unsigned page_idx;
+	int ret;
+
+	if (mapping->a_ops->readpages) {
+		ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
+		/* Clean up the remaining pages */
+		put_pages_list(pages);
+		goto out;
+	}
+
+	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
+		struct page *page = list_to_page(pages);
+		list_del(&page->lru);
+		if (!add_to_page_cache_lru(page, mapping,
+					page->index, GFP_KERNEL)) {
+			mapping->a_ops->readpage(filp, page);
+		}
+		page_cache_release(page);
+	}
+	ret = 0;
+out:
+	return ret;
+}
+
+/*
+ * do_page_cache_readahead actually reads a chunk of disk.  It allocates all
+ * the pages first, then submits them all for I/O. This avoids the very bad
+ * behaviour which would occur if page allocations are causing VM writeback.
+ * We really don't want to intermingle reads and writes like that.
+ *
+ * Returns the number of pages requested, or the maximum amount of I/O allowed.
+ *
+ * do_page_cache_readahead() returns -1 if it encountered request queue
+ * congestion.
+ */
+static int
+__do_page_cache_readahead(struct address_space *mapping, struct file *filp,
+			pgoff_t offset, unsigned long nr_to_read,
+			unsigned long lookahead_size)
+{
+	struct inode *inode = mapping->host;
+	struct page *page;
+	unsigned long end_index;	/* The last page we want to read */
+	LIST_HEAD(page_pool);
+	int page_idx;
+	int ret = 0;
+	loff_t isize = i_size_read(inode);
+
+	if (isize == 0)
+		goto out;
+
+	end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);
+
+	/*
+	 * Preallocate as many pages as we will need.
+	 */
+	for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
+		pgoff_t page_offset = offset + page_idx;
+
+		if (page_offset > end_index)
+			break;
+
+		rcu_read_lock();
+		page = radix_tree_lookup(&mapping->page_tree, page_offset);
+		rcu_read_unlock();
+		if (page)
+			continue;
+
+		page = page_cache_alloc_cold(mapping);
+		if (!page)
+			break;
+		page->index = page_offset;
+		list_add(&page->lru, &page_pool);
+		if (page_idx == nr_to_read - lookahead_size)
+			SetPageReadahead(page);
+		ret++;
+	}
+
+	/*
+	 * Now start the IO.  We ignore I/O errors - if the page is not
+	 * uptodate then the caller will launch readpage again, and
+	 * will then handle the error.
+	 */
+	if (ret)
+		read_pages(mapping, filp, &page_pool, ret);
+	BUG_ON(!list_empty(&page_pool));
+out:
+	return ret;
+}
+
+/*
+ * Chunk the readahead into 2 megabyte units, so that we don't pin too much
+ * memory at once.
+ */
+int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
+		pgoff_t offset, unsigned long nr_to_read)
+{
+	int ret = 0;
+
+	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
+		return -EINVAL;
+
+	while (nr_to_read) {
+		int err;
+
+		unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE;
+
+		if (this_chunk > nr_to_read)
+			this_chunk = nr_to_read;
+		err = __do_page_cache_readahead(mapping, filp,
+						offset, this_chunk, 0);
+		if (err < 0) {
+			ret = err;
+			break;
+		}
+		ret += err;
+		offset += this_chunk;
+		nr_to_read -= this_chunk;
+	}
+	return ret;
+}
+
+/*
+ * This version skips the IO if the queue is read-congested, and will tell the
+ * block layer to abandon the readahead if request allocation would block.
+ *
+ * force_page_cache_readahead() will ignore queue congestion and will block on
+ * request queues.
+ */
+int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
+			pgoff_t offset, unsigned long nr_to_read)
+{
+	if (bdi_read_congested(mapping->backing_dev_info))
+		return -1;
+
+	return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0);
+}
+
+/*
+ * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
+ * sensible upper limit.
+ */
+unsigned long max_sane_readahead(unsigned long nr)
+{
+	return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE_FILE)
+		+ node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
+}
+
+static int __init readahead_init(void)
+{
+	int err;
+
+	err = bdi_init(&default_backing_dev_info);
+	if (!err)
+		bdi_register(&default_backing_dev_info, NULL, "default");
+
+	return err;
+}
+subsys_initcall(readahead_init);
+
+/*
+ * Submit IO for the read-ahead request in file_ra_state.
+ */
+static unsigned long ra_submit(struct file_ra_state *ra,
+		       struct address_space *mapping, struct file *filp)
+{
+	int actual;
+
+	actual = __do_page_cache_readahead(mapping, filp,
+					ra->start, ra->size, ra->async_size);
+
+	return actual;
+}
+
+/*
+ * Set the initial window size, round to next power of 2 and square
+ * for small size, x 4 for medium, and x 2 for large
+ * for 128k (32 page) max ra
+ * 1-8 page = 32k initial, > 8 page = 128k initial
+ */
+static unsigned long get_init_ra_size(unsigned long size, unsigned long max)
+{
+	unsigned long newsize = roundup_pow_of_two(size);
+
+	if (newsize <= max / 32)
+		newsize = newsize * 4;
+	else if (newsize <= max / 4)
+		newsize = newsize * 2;
+	else
+		newsize = max;
+
+	return newsize;
+}
+
+/*
+ *  Get the previous window size, ramp it up, and
+ *  return it as the new window size.
+ */
+static unsigned long get_next_ra_size(struct file_ra_state *ra,
+						unsigned long max)
+{
+	unsigned long cur = ra->size;
+	unsigned long newsize;
+
+	if (cur < max / 16)
+		newsize = 4 * cur;
+	else
+		newsize = 2 * cur;
+
+	return min(newsize, max);
+}
+
+/*
+ * On-demand readahead design.
+ *
+ * The fields in struct file_ra_state represent the most-recently-executed
+ * readahead attempt:
+ *
+ *                        |<----- 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 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 (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.
+ *
+ * prev_pos tracks the last visited byte in the _previous_ read request.
+ * It should be maintained by the caller, and will be used for detecting
+ * small random reads. Note that the readahead algorithm checks loosely
+ * for sequential patterns. Hence interleaved reads might be served as
+ * sequential ones.
+ *
+ * There is a special-case: if the first page which the application tries to
+ * read happens to be the first page of the file, it is assumed that a linear
+ * read is about to happen and the window is immediately set to the initial size
+ * based on I/O request size and the max_readahead.
+ *
+ * The code ramps up the readahead size aggressively at first, but slow down as
+ * it approaches max_readhead.
+ */
+
+/*
+ * A minimal readahead algorithm for trivial sequential/random reads.
+ */
+static unsigned long
+ondemand_readahead(struct address_space *mapping,
+		   struct file_ra_state *ra, struct file *filp,
+		   bool hit_readahead_marker, pgoff_t offset,
+		   unsigned long req_size)
+{
+	int	max = ra->ra_pages;	/* max readahead pages */
+	pgoff_t prev_offset;
+	int	sequential;
+
+	/*
+	 * It's the expected callback offset, assume sequential access.
+	 * Ramp up sizes, and push forward the readahead window.
+	 */
+	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;
+	}
+
+	prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT;
+	sequential = offset - prev_offset <= 1UL || req_size > max;
+
+	/*
+	 * Standalone, small read.
+	 * Read as is, and do not pollute the readahead state.
+	 */
+	if (!hit_readahead_marker && !sequential) {
+		return __do_page_cache_readahead(mapping, filp,
+						offset, req_size, 0);
+	}
+
+	/*
+	 * Hit a marked page without valid readahead state.
+	 * E.g. interleaved reads.
+	 * Query the pagecache for async_size, which normally equals to
+	 * readahead size. Ramp it up and use it as the new readahead size.
+	 */
+	if (hit_readahead_marker) {
+		pgoff_t start;
+
+		rcu_read_lock();
+		start = radix_tree_next_hole(&mapping->page_tree, offset,max+1);
+		rcu_read_unlock();
+
+		if (!start || start - offset > max)
+			return 0;
+
+		ra->start = start;
+		ra->size = start - offset;	/* old async_size */
+		ra->size = get_next_ra_size(ra, max);
+		ra->async_size = ra->size;
+		goto readit;
+	}
+
+	/*
+	 * It may be one of
+	 * 	- first read on start of file
+	 * 	- sequential cache miss
+	 * 	- oversize random read
+	 * Start readahead for it.
+	 */
+	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;
+
+readit:
+	return ra_submit(ra, mapping, filp);
+}
+
+/**
+ * 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()
+ * @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_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.
+ */
+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;
+
+	/* 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 */
+	ondemand_readahead(mapping, ra, filp, true, offset, req_size);
+}
+EXPORT_SYMBOL_GPL(page_cache_async_readahead);