1 files changed, 98 insertions, 178 deletions

diff --git a/mm/readahead.c b/mm/readahead.c
index 817b2a352d78..517c0be7ce66 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -313,7 +313,7 @@ void force_page_cache_ra(struct readahead_control *ractl,
 	struct address_space *mapping = ractl->mapping;
 	struct file_ra_state *ra = ractl->ra;
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
-	unsigned long max_pages, index;
+	unsigned long max_pages;
 
 	if (unlikely(!mapping->a_ops->read_folio && !mapping->a_ops->readahead))
 		return;
@@ -322,7 +322,6 @@ void force_page_cache_ra(struct readahead_control *ractl,
 	 * If the request exceeds the readahead window, allow the read to
 	 * be up to the optimal hardware IO size
 	 */
-	index = readahead_index(ractl);
 	max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
 	nr_to_read = min_t(unsigned long, nr_to_read, max_pages);
 	while (nr_to_read) {
@@ -330,10 +329,8 @@ void force_page_cache_ra(struct readahead_control *ractl,
 
 		if (this_chunk > nr_to_read)
 			this_chunk = nr_to_read;
-		ractl->_index = index;
 		do_page_cache_ra(ractl, this_chunk, 0);
 
-		index += this_chunk;
 		nr_to_read -= this_chunk;
 	}
 }
@@ -413,58 +410,6 @@ static unsigned long get_next_ra_size(struct file_ra_state *ra,
  * it approaches max_readhead.
  */
 
-/*
- * Count contiguously cached pages from @index-1 to @index-@max,
- * this count is a conservative estimation of
- * 	- length of the sequential read sequence, or
- * 	- thrashing threshold in memory tight systems
- */
-static pgoff_t count_history_pages(struct address_space *mapping,
-				   pgoff_t index, unsigned long max)
-{
-	pgoff_t head;
-
-	rcu_read_lock();
-	head = page_cache_prev_miss(mapping, index - 1, max);
-	rcu_read_unlock();
-
-	return index - 1 - head;
-}
-
-/*
- * page cache context based readahead
- */
-static int try_context_readahead(struct address_space *mapping,
-				 struct file_ra_state *ra,
-				 pgoff_t index,
-				 unsigned long req_size,
-				 unsigned long max)
-{
-	pgoff_t size;
-
-	size = count_history_pages(mapping, index, max);
-
-	/*
-	 * not enough history pages:
-	 * it could be a random read
-	 */
-	if (size <= req_size)
-		return 0;
-
-	/*
-	 * starts from beginning of file:
-	 * it is a strong indication of long-run stream (or whole-file-read)
-	 */
-	if (size >= index)
-		size *= 2;
-
-	ra->start = index;
-	ra->size = min(size + req_size, max);
-	ra->async_size = 1;
-
-	return 1;
-}
-
 static inline int ra_alloc_folio(struct readahead_control *ractl, pgoff_t index,
 		pgoff_t mark, unsigned int order, gfp_t gfp)
 {
@@ -491,7 +436,8 @@ void page_cache_ra_order(struct readahead_control *ractl,
 		struct file_ra_state *ra, unsigned int new_order)
 {
 	struct address_space *mapping = ractl->mapping;
-	pgoff_t index = readahead_index(ractl);
+	pgoff_t start = readahead_index(ractl);
+	pgoff_t index = start;
 	pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
 	pgoff_t mark = index + ra->size - ra->async_size;
 	unsigned int nofs;
@@ -527,11 +473,6 @@ void page_cache_ra_order(struct readahead_control *ractl,
 		index += 1UL << order;
 	}
 
-	if (index > limit) {
-		ra->size += index - limit - 1;
-		ra->async_size += index - limit - 1;
-	}
-
 	read_pages(ractl);
 	filemap_invalidate_unlock_shared(mapping);
 	memalloc_nofs_restore(nofs);
@@ -544,22 +485,14 @@ void page_cache_ra_order(struct readahead_control *ractl,
 	if (!err)
 		return;
 fallback:
-	do_page_cache_ra(ractl, ra->size, ra->async_size);
+	do_page_cache_ra(ractl, ra->size - (index - start), ra->async_size);
 }
 
-/*
- * A minimal readahead algorithm for trivial sequential/random reads.
- */
-static void ondemand_readahead(struct readahead_control *ractl,
-		struct folio *folio, unsigned long req_size)
+static unsigned long ractl_max_pages(struct readahead_control *ractl,
+		unsigned long req_size)
 {
 	struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
-	struct file_ra_state *ra = ractl->ra;
-	unsigned long max_pages = ra->ra_pages;
-	unsigned long add_pages;
-	pgoff_t index = readahead_index(ractl);
-	pgoff_t expected, prev_index;
-	unsigned int order = folio ? folio_order(folio) : 0;
+	unsigned long max_pages = ractl->ra->ra_pages;
 
 	/*
 	 * If the request exceeds the readahead window, allow the read to
@@ -567,112 +500,17 @@ static void ondemand_readahead(struct readahead_control *ractl,
 	 */
 	if (req_size > max_pages && bdi->io_pages > max_pages)
 		max_pages = min(req_size, bdi->io_pages);
-
-	/*
-	 * start of file
-	 */
-	if (!index)
-		goto initial_readahead;
-
-	/*
-	 * It's the expected callback index, assume sequential access.
-	 * Ramp up sizes, and push forward the readahead window.
-	 */
-	expected = round_down(ra->start + ra->size - ra->async_size,
-			1UL << order);
-	if (index == expected || index == (ra->start + ra->size)) {
-		ra->start += ra->size;
-		ra->size = get_next_ra_size(ra, max_pages);
-		ra->async_size = ra->size;
-		goto readit;
-	}
-
-	/*
-	 * Hit a marked folio 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 (folio) {
-		pgoff_t start;
-
-		rcu_read_lock();
-		start = page_cache_next_miss(ractl->mapping, index + 1,
-				max_pages);
-		rcu_read_unlock();
-
-		if (!start || start - index > max_pages)
-			return;
-
-		ra->start = start;
-		ra->size = start - index;	/* old async_size */
-		ra->size += req_size;
-		ra->size = get_next_ra_size(ra, max_pages);
-		ra->async_size = ra->size;
-		goto readit;
-	}
-
-	/*
-	 * oversize read
-	 */
-	if (req_size > max_pages)
-		goto initial_readahead;
-
-	/*
-	 * sequential cache miss
-	 * trivial case: (index - prev_index) == 1
-	 * unaligned reads: (index - prev_index) == 0
-	 */
-	prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
-	if (index - prev_index <= 1UL)
-		goto initial_readahead;
-
-	/*
-	 * Query the page cache and look for the traces(cached history pages)
-	 * that a sequential stream would leave behind.
-	 */
-	if (try_context_readahead(ractl->mapping, ra, index, req_size,
-			max_pages))
-		goto readit;
-
-	/*
-	 * standalone, small random read
-	 * Read as is, and do not pollute the readahead state.
-	 */
-	do_page_cache_ra(ractl, req_size, 0);
-	return;
-
-initial_readahead:
-	ra->start = index;
-	ra->size = get_init_ra_size(req_size, max_pages);
-	ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;
-
-readit:
-	/*
-	 * Will this read hit the readahead marker made by itself?
-	 * If so, trigger the readahead marker hit now, and merge
-	 * the resulted next readahead window into the current one.
-	 * Take care of maximum IO pages as above.
-	 */
-	if (index == ra->start && ra->size == ra->async_size) {
-		add_pages = get_next_ra_size(ra, max_pages);
-		if (ra->size + add_pages <= max_pages) {
-			ra->async_size = add_pages;
-			ra->size += add_pages;
-		} else {
-			ra->size = max_pages;
-			ra->async_size = max_pages >> 1;
-		}
-	}
-
-	ractl->_index = ra->start;
-	page_cache_ra_order(ractl, ra, order);
+	return max_pages;
 }
 
 void page_cache_sync_ra(struct readahead_control *ractl,
 		unsigned long req_count)
 {
+	pgoff_t index = readahead_index(ractl);
 	bool do_forced_ra = ractl->file && (ractl->file->f_mode & FMODE_RANDOM);
+	struct file_ra_state *ra = ractl->ra;
+	unsigned long max_pages, contig_count;
+	pgoff_t prev_index, miss;
 
 	/*
 	 * Even if readahead is disabled, issue this request as readahead
@@ -680,7 +518,7 @@ void page_cache_sync_ra(struct readahead_control *ractl,
 	 * readahead will do the right thing and limit the read to just the
 	 * requested range, which we'll set to 1 page for this case.
 	 */
-	if (!ractl->ra->ra_pages || blk_cgroup_congested()) {
+	if (!ra->ra_pages || blk_cgroup_congested()) {
 		if (!ractl->file)
 			return;
 		req_count = 1;
@@ -693,15 +531,63 @@ void page_cache_sync_ra(struct readahead_control *ractl,
 		return;
 	}
 
-	ondemand_readahead(ractl, NULL, req_count);
+	max_pages = ractl_max_pages(ractl, req_count);
+	prev_index = (unsigned long long)ra->prev_pos >> PAGE_SHIFT;
+	/*
+	 * A start of file, oversized read, or sequential cache miss:
+	 * trivial case: (index - prev_index) == 1
+	 * unaligned reads: (index - prev_index) == 0
+	 */
+	if (!index || req_count > max_pages || index - prev_index <= 1UL) {
+		ra->start = index;
+		ra->size = get_init_ra_size(req_count, max_pages);
+		ra->async_size = ra->size > req_count ? ra->size - req_count :
+							ra->size >> 1;
+		goto readit;
+	}
+
+	/*
+	 * Query the page cache and look for the traces(cached history pages)
+	 * that a sequential stream would leave behind.
+	 */
+	rcu_read_lock();
+	miss = page_cache_prev_miss(ractl->mapping, index - 1, max_pages);
+	rcu_read_unlock();
+	contig_count = index - miss - 1;
+	/*
+	 * Standalone, small random read. Read as is, and do not pollute the
+	 * readahead state.
+	 */
+	if (contig_count <= req_count) {
+		do_page_cache_ra(ractl, req_count, 0);
+		return;
+	}
+	/*
+	 * File cached from the beginning:
+	 * it is a strong indication of long-run stream (or whole-file-read)
+	 */
+	if (miss == ULONG_MAX)
+		contig_count *= 2;
+	ra->start = index;
+	ra->size = min(contig_count + req_count, max_pages);
+	ra->async_size = 1;
+readit:
+	ractl->_index = ra->start;
+	page_cache_ra_order(ractl, ra, 0);
 }
 EXPORT_SYMBOL_GPL(page_cache_sync_ra);
 
 void page_cache_async_ra(struct readahead_control *ractl,
 		struct folio *folio, unsigned long req_count)
 {
+	unsigned long max_pages;
+	struct file_ra_state *ra = ractl->ra;
+	pgoff_t index = readahead_index(ractl);
+	pgoff_t expected, start;
+	unsigned int order = folio_order(folio);
+
 	/* no readahead */
-	if (!ractl->ra->ra_pages)
+	if (!ra->ra_pages)
 		return;
 
 	/*
@@ -715,7 +601,41 @@ void page_cache_async_ra(struct readahead_control *ractl,
 	if (blk_cgroup_congested())
 		return;
 
-	ondemand_readahead(ractl, folio, req_count);
+	max_pages = ractl_max_pages(ractl, req_count);
+	/*
+	 * It's the expected callback index, assume sequential access.
+	 * Ramp up sizes, and push forward the readahead window.
+	 */
+	expected = round_down(ra->start + ra->size - ra->async_size,
+			1UL << order);
+	if (index == expected) {
+		ra->start += ra->size;
+		ra->size = get_next_ra_size(ra, max_pages);
+		ra->async_size = ra->size;
+		goto readit;
+	}
+
+	/*
+	 * Hit a marked folio 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.
+	 */
+	rcu_read_lock();
+	start = page_cache_next_miss(ractl->mapping, index + 1, max_pages);
+	rcu_read_unlock();
+
+	if (!start || start - index > max_pages)
+		return;
+
+	ra->start = start;
+	ra->size = start - index;	/* old async_size */
+	ra->size += req_count;
+	ra->size = get_next_ra_size(ra, max_pages);
+	ra->async_size = ra->size;
+readit:
+	ractl->_index = ra->start;
+	page_cache_ra_order(ractl, ra, order);
 }
 EXPORT_SYMBOL_GPL(page_cache_async_ra);