Currently extent_readpages (called from btrfs_redpages) will always call
__extent_readpages which tries to create contiguous range of pages and
call __do_contiguous_readpages when such contiguous range is created.
It turns out this is unnecessary due to the fact that generic VFS code
always calls filesystem's ->readpages callback (btrfs_readpages in
this case) with already contiguous pages. Armed with this knowledge it's
possible to simplify extent_readpages by eliminating the call to
__extent_readpages and directly calling contiguous_readpages. The only
edge case that needs to be handled is when add_to_page_cache_lru
fails. This is easy as all that is needed is to submit whatever is the
number of pages successfully added to the lru.
Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
---
I've been running with this patch for the past 3 months and haven't encountered
any issues with it.
fs/btrfs/extent_io.c | 58 +++++++++++---------------------------------
1 file changed, 14 insertions(+), 44 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index b20700ad8752..551dd21d7351 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3066,7 +3066,7 @@ static int __do_readpage(struct extent_io_tree *tree,
return ret;
}
-static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
+static inline void contiguous_readpages(struct extent_io_tree *tree,
struct page *pages[], int nr_pages,
u64 start, u64 end,
struct extent_map **em_cached,
@@ -3097,46 +3097,6 @@ static inline void __do_contiguous_readpages(struct extent_io_tree *tree,
}
}
-static void __extent_readpages(struct extent_io_tree *tree,
- struct page *pages[],
- int nr_pages,
- struct extent_map **em_cached,
- struct bio **bio, unsigned long *bio_flags,
- u64 *prev_em_start)
-{
- u64 start = 0;
- u64 end = 0;
- u64 page_start;
- int index;
- int first_index = 0;
-
- for (index = 0; index < nr_pages; index++) {
- page_start = page_offset(pages[index]);
- if (!end) {
- start = page_start;
- end = start + PAGE_SIZE - 1;
- first_index = index;
- } else if (end + 1 == page_start) {
- end += PAGE_SIZE;
- } else {
- __do_contiguous_readpages(tree, &pages[first_index],
- index - first_index, start,
- end, em_cached,
- bio, bio_flags,
- prev_em_start);
- start = page_start;
- end = start + PAGE_SIZE - 1;
- first_index = index;
- }
- }
-
- if (end)
- __do_contiguous_readpages(tree, &pages[first_index],
- index - first_index, start,
- end, em_cached, bio,
- bio_flags, prev_em_start);
-}
-
static int __extent_read_full_page(struct extent_io_tree *tree,
struct page *page,
get_extent_t *get_extent,
@@ -4098,6 +4058,8 @@ int extent_readpages(struct address_space *mapping, struct list_head *pages,
u64 prev_em_start = (u64)-1;
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);
@@ -4106,14 +4068,22 @@ int extent_readpages(struct address_space *mapping, struct list_head *pages,
if (add_to_page_cache_lru(page, mapping, page->index,
readahead_gfp_mask(mapping))) {
put_page(page);
- continue;
+ break;
}
pagepool[nr++] = page;
+ contig_end = page_offset(page) + PAGE_SIZE - 1;
}
- __extent_readpages(tree, pagepool, nr, &em_cached, &bio,
- &bio_flags, &prev_em_start);
+ if (nr) {
+ u64 contig_start = page_offset(pagepool[0]);
+
+ 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);
+ }
}
if (em_cached)
--
2.17.1
