[PATCH v6 09/16] btrfs: Convert from readpages to readahead

Matthew Wilcox
2020-02-17T18:48:50Z

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

Use the new readahead operation in btrfs. Add a
readahead_for_each_batch() iterator to optimise the loop in the XArray.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
fs/btrfs/extent_io.c | 48 ++++++++++++++---------------------------
fs/btrfs/extent_io.h | 3 +--
fs/btrfs/inode.c | 16 ++++++--------
include/linux/pagemap.h | 27 +++++++++++++++++++++++
4 files changed, 51 insertions(+), 43 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c0f202741e09..d9f66058e0a7 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4278,52 +4278,36 @@ 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;
- }
-
- if (nr) {
- u64 contig_start = page_offset(pagepool[0]);
+ readahead_for_each_batch(rac, pagepool, ARRAY_SIZE(pagepool), nr) {
+ u64 contig_start = page_offset(pagepool[0]);
+ u64 contig_end = page_offset(pagepool[nr - 1]) + PAGE_SIZE - 1;

- 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) {
+ int ret = submit_one_bio(bio, 0, bio_flags);
+ if (ret < 0) {
+ /* XXX: unlock the pages here? */
+ }
+ }
}

/*
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 5b3ec93ff911..d964b2a78ed8 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -4794,8 +4794,8 @@ 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
@@ -6996,11 +6996,11 @@ 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.
*/
@@ -8239,11 +8239,9 @@ 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)
@@ -10448,7 +10446,7 @@ 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,
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 4f36c06d064d..1bbb60a0bf16 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -669,6 +669,33 @@ static inline void readahead_next(struct readahead_control *rac)
#define readahead_for_each(rac, page) \
for (; (page = readahead_page(rac)); readahead_next(rac))

+static inline unsigned int readahead_page_batch(struct readahead_control *rac,
+ struct page **array, unsigned int size)
+{
+ unsigned int batch = 0;
+ XA_STATE(xas, &rac->mapping->i_pages, rac->_start);
+ struct page *page;
+
+ rac->_batch_count = 0;
+ xas_for_each(&xas, page, rac->_start + rac->_nr_pages - 1) {
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ VM_BUG_ON_PAGE(PageTail(page), page);
+ array[batch++] = page;
+ rac->_batch_count += hpage_nr_pages(page);
+ if (PageHead(page))
+ xas_set(&xas, rac->_start + rac->_batch_count);
+
+ if (batch == size)
+ break;
+ }
+
+ return batch;
+}
+
+#define readahead_for_each_batch(rac, array, size, nr) \
+ for (; (nr = readahead_page_batch(rac, array, size)); \
+ readahead_next(rac))
+
/* The byte offset into the file of this readahead block */
static inline loff_t readahead_offset(struct readahead_control *rac)
{
--
2.25.0