Ocfs2 devel - Feb 2020 - [PATCH v8 17/25] btrfs: Convert from readpages to readahead

From: "Matthew Wilcox (Oracle)" <willy at infradead.org>

Implement the new readahead method in btrfs.  Add a readahead_page_batch()
to optimise fetching a batch of pages at once.

Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org>
---
 fs/btrfs/extent_io.c | 46 ++++++++++++++------------------------------
 fs/btrfs/extent_io.h |  3 +--
 fs/btrfs/inode.c     | 16 +++++++--------
 3 files changed, 22 insertions(+), 43 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c0f202741e09..e70f14c1de60 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4278,52 +4278,34 @@ int extent_writepages(struct address_space *mapping,
 	return ret;
 }
 
-int extent_readpages(struct address_space *mapping, struct list_head *pages,
-		     unsigned nr_pages)
+void extent_readahead(struct readahead_control *rac)
 {
 	struct bio *bio = NULL;
 	unsigned long bio_flags = 0;
 	struct page *pagepool[16];
 	struct extent_map *em_cached = NULL;
-	struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree;
-	int nr = 0;
+	struct extent_io_tree *tree =
&BTRFS_I(rac->mapping->host)->io_tree;
 	u64 prev_em_start = (u64)-1;
+	int nr;
 
-	while (!list_empty(pages)) {
-		u64 contig_end = 0;
-
-		for (nr = 0; nr < ARRAY_SIZE(pagepool) && !list_empty(pages);) {
-			struct page *page = lru_to_page(pages);
-
-			prefetchw(&page->flags);
-			list_del(&page->lru);
-			if (add_to_page_cache_lru(page, mapping, page->index,
-						readahead_gfp_mask(mapping))) {
-				put_page(page);
-				break;
-			}
-
-			pagepool[nr++] = page;
-			contig_end = page_offset(page) + PAGE_SIZE - 1;
-		}
+	while ((nr = readahead_page_batch(rac, pagepool))) {
+		u64 contig_start = page_offset(pagepool[0]);
+		u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1;
 
-		if (nr) {
-			u64 contig_start = page_offset(pagepool[0]);
+		ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end);
 
-			ASSERT(contig_start + nr * PAGE_SIZE - 1 == contig_end);
-
-			contiguous_readpages(tree, pagepool, nr, contig_start,
-				     contig_end, &em_cached, &bio, &bio_flags,
-				     &prev_em_start);
-		}
+		contiguous_readpages(tree, pagepool, nr, contig_start,
+				contig_end, &em_cached, &bio, &bio_flags,
+				&prev_em_start);
 	}
 
 	if (em_cached)
 		free_extent_map(em_cached);
 
-	if (bio)
-		return submit_one_bio(bio, 0, bio_flags);
-	return 0;
+	if (bio) {
+		if (submit_one_bio(bio, 0, bio_flags))
+			return;
+	}
 }
 
 /*
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 5d205bbaafdc..bddac32948c7 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -198,8 +198,7 @@ int extent_writepages(struct address_space *mapping,
 		      struct writeback_control *wbc);
 int btree_write_cache_pages(struct address_space *mapping,
 			    struct writeback_control *wbc);
-int extent_readpages(struct address_space *mapping, struct list_head *pages,
-		     unsigned nr_pages);
+void extent_readahead(struct readahead_control *rac);
 int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		__u64 start, __u64 len);
 void set_page_extent_mapped(struct page *page);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 7d26b4bfb2c6..61d5137ce4e9 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4802,8 +4802,8 @@ static void evict_inode_truncate_pages(struct inode
*inode)
 
 	/*
 	 * Keep looping until we have no more ranges in the io tree.
-	 * We can have ongoing bios started by readpages (called from readahead)
-	 * that have their endio callback (extent_io.c:end_bio_extent_readpage)
+	 * We can have ongoing bios started by readahead that have
+	 * their endio callback (extent_io.c:end_bio_extent_readpage)
 	 * still in progress (unlocked the pages in the bio but did not yet
 	 * unlocked the ranges in the io tree). Therefore this means some
 	 * ranges can still be locked and eviction started because before
@@ -7004,11 +7004,11 @@ static int lock_extent_direct(struct inode *inode, u64
lockstart, u64 lockend,
 			 * for it to complete) and then invalidate the pages for
 			 * this range (through invalidate_inode_pages2_range()),
 			 * but that can lead us to a deadlock with a concurrent
-			 * call to readpages() (a buffered read or a defrag call
+			 * call to readahead (a buffered read or a defrag call
 			 * triggered a readahead) on a page lock due to an
 			 * ordered dio extent we created before but did not have
 			 * yet a corresponding bio submitted (whence it can not
-			 * complete), which makes readpages() wait for that
+			 * complete), which makes readahead wait for that
 			 * ordered extent to complete while holding a lock on
 			 * that page.
 			 */
@@ -8247,11 +8247,9 @@ static int btrfs_writepages(struct address_space
*mapping,
 	return extent_writepages(mapping, wbc);
 }
 
-static int
-btrfs_readpages(struct file *file, struct address_space *mapping,
-		struct list_head *pages, unsigned nr_pages)
+static void btrfs_readahead(struct readahead_control *rac)
 {
-	return extent_readpages(mapping, pages, nr_pages);
+	extent_readahead(rac);
 }
 
 static int __btrfs_releasepage(struct page *page, gfp_t gfp_flags)
@@ -10456,7 +10454,7 @@ static const struct address_space_operations btrfs_aops
= {
 	.readpage	= btrfs_readpage,
 	.writepage	= btrfs_writepage,
 	.writepages	= btrfs_writepages,
-	.readpages	= btrfs_readpages,
+	.readahead	= btrfs_readahead,
 	.direct_IO	= btrfs_direct_IO,
 	.invalidatepage = btrfs_invalidatepage,
 	.releasepage	= btrfs_releasepage,
-- 
2.25.0

On Tue, Feb 25, 2020 at 01:48:30PM -0800, Matthew Wilcox
wrote:
> From: "Matthew Wilcox (Oracle)" <willy at infradead.org>
> 
> Implement the new readahead method in btrfs.  Add a readahead_page_batch()
> to optimise fetching a batch of pages at once.
readahead_page_batch() isn't added in this patch anymore.

Otherwise this looks good to me, although I don't feel confident
enough to give a Reviewed-by for btrfs code.