[PATCH v6 21/22] erofs: implement fscache-based data readahead

Jeffle Xu
2022-03-25T12:24:10Z

Implements fscache-based data readahead. Also registers an individual
bdi for each erofs instance to enable readahead.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
fs/erofs/fscache.c | 114 +++++++++++++++++++++++++++++++++++++++++++++
fs/erofs/super.c | 4 ++
2 files changed, 118 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index cbb39657615e..589d1e7c2b1b 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -191,12 +191,126 @@ static int erofs_fscache_readpage(struct file *file, struct page *page)
return ret;
}

+static inline size_t erofs_fscache_calc_len(struct erofs_map_blocks *map,
+ size_t len, size_t done)
+{
+ /*
+ * 1) For CHUNK_BASED layout, the output m_la is rounded down to the
+ * nearest chunk boundary, and the output m_llen actually starts from
+ * the start of the containing chunk.
+ * 2) For other cases, the output m_la is equal to o_la.
+ */
+ size_t length = map->m_llen - (map->o_la - map->m_la);
+
+ return min_t(size_t, length, len - done);
+}
+
+static inline void erofs_fscache_unlock_folios(struct readahead_control *rac,
+ size_t len)
+{
+ while (len) {
+ struct folio *folio = readahead_folio(rac);
+
+ len -= folio_size(folio);
+ folio_mark_uptodate(folio);
+ folio_unlock(folio);
+ }
+}
+
+static void erofs_fscache_readahead(struct readahead_control *rac)
+{
+ struct inode *inode = rac->mapping->host;
+ struct erofs_inode *vi = EROFS_I(inode);
+ struct super_block *sb = inode->i_sb;
+ size_t len, done = 0;
+ loff_t start;
+ int ret;
+
+ if (erofs_inode_is_data_compressed(vi->datalayout)) {
+ erofs_info(sb, "compressed layout not supported yet");
+ return;
+ }
+
+ if (!readahead_count(rac))
+ return;
+
+ start = readahead_pos(rac);
+ len = readahead_length(rac);
+
+ do {
+ struct erofs_map_blocks map;
+
+ map.m_la = map.o_la = start + done;
+
+ ret = erofs_map_blocks(inode, &map, EROFS_GET_BLOCKS_RAW);
+ if (ret)
+ return;
+
+ /* Read-ahead Hole
+ * Two cases will hit this:
+ * 1) EOF. Imposibble in readahead routine;
+ * 2) hole. Only CHUNK_BASED layout supports hole.
+ */
+ if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+ struct iov_iter iter;
+ loff_t offset = start + done;
+ size_t count = erofs_fscache_calc_len(&map, len, done);
+
+ iov_iter_xarray(&iter, READ, &rac->mapping->i_pages, offset, count);
+ iov_iter_zero(count, &iter);
+
+ erofs_fscache_unlock_folios(rac, count);
+ ret = count;
+ continue;
+ }
+
+ ret = erofs_fscache_get_map(&map, sb);
+ if (ret)
+ return;
+
+ /* Read-ahead Inline */
+ if (map.m_flags & EROFS_MAP_META) {
+ struct folio *folio = readahead_folio(rac);
+
+ ret = erofs_fscache_readpage_inline(folio, &map);
+ if (!ret) {
+ folio_mark_uptodate(folio);
+ ret = folio_size(folio);
+ }
+
+ folio_unlock(folio);
+ continue;
+ }
+
+ /* Read-ahead No-inline */
+ if (vi->datalayout == EROFS_INODE_FLAT_PLAIN ||
+ vi->datalayout == EROFS_INODE_FLAT_INLINE ||
+ vi->datalayout == EROFS_INODE_CHUNK_BASED) {
+ struct fscache_cookie *cookie = map.m_fscache->cookie;
+ loff_t offset = start + done;
+ size_t count = erofs_fscache_calc_len(&map, len, done);
+ loff_t pstart = map.m_pa + (map.o_la - map.m_la);
+
+ ret = erofs_fscache_read_folios(cookie, rac->mapping,
+ offset, count, pstart);
+ if (!ret) {
+ erofs_fscache_unlock_folios(rac, count);
+ ret = count;
+ }
+ } else {
+ DBG_BUGON(1);
+ return;
+ }
+ } while (ret > 0 && ((done += ret) < len));
+}
+
static const struct address_space_operations erofs_fscache_blob_aops = {
.readpage = erofs_fscache_readpage_blob,
};

const struct address_space_operations erofs_fscache_access_aops = {
.readpage = erofs_fscache_readpage,
+ .readahead = erofs_fscache_readahead,
};

/*
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 9a6f35e0c22b..8ac400581784 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -619,6 +619,10 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
return PTR_ERR(bootstrap);

sbi->bootstrap = bootstrap;
+
+ err = super_setup_bdi(sb);
+ if (err)
+ return err;
}

err = erofs_read_superblock(sb);
--
2.27.0