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Subject[PATCH v4 20/21] erofs: implement fscache-based data readahead
Date
This patch 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 | 153 +++++++++++++++++++++++++++++++++++++++++++++
fs/erofs/super.c | 4 ++
2 files changed, 157 insertions(+)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 89c533ad965e..19f44ee01852 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -10,6 +10,13 @@ struct erofs_fscache_map {
u64 m_llen;
};

+struct erofs_fscahce_ra_ctx {
+ struct readahead_control *rac;
+ struct address_space *mapping;
+ loff_t start;
+ size_t len, done;
+};
+
static struct fscache_volume *volume;

/*
@@ -199,12 +206,158 @@ static int erofs_fscache_readpage(struct file *file, struct page *page)
return ret;
}

+static inline size_t erofs_fscache_calc_len(struct erofs_fscahce_ra_ctx *ractx,
+ struct erofs_fscache_map *fsmap)
+{
+ /*
+ * 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 len = fsmap->m_llen - (fsmap->o_la - fsmap->m_la);
+
+ return min_t(size_t, len, ractx->len - ractx->done);
+}
+
+static inline void erofs_fscache_unlock_pages(struct readahead_control *rac,
+ size_t len)
+{
+ while (len) {
+ struct page *page = readahead_page(rac);
+
+ SetPageUptodate(page);
+ unlock_page(page);
+ put_page(page);
+
+ len -= PAGE_SIZE;
+ }
+}
+
+static int erofs_fscache_ra_hole(struct erofs_fscahce_ra_ctx *ractx,
+ struct erofs_fscache_map *fsmap)
+{
+ struct iov_iter iter;
+ loff_t start = ractx->start + ractx->done;
+ size_t length = erofs_fscache_calc_len(ractx, fsmap);
+
+ iov_iter_xarray(&iter, READ, &ractx->mapping->i_pages, start, length);
+ iov_iter_zero(length, &iter);
+
+ erofs_fscache_unlock_pages(ractx->rac, length);
+ return length;
+}
+
+static int erofs_fscache_ra_noinline(struct erofs_fscahce_ra_ctx *ractx,
+ struct erofs_fscache_map *fsmap)
+{
+ struct fscache_cookie *cookie = fsmap->m_ctx->cookie;
+ loff_t start = ractx->start + ractx->done;
+ size_t length = erofs_fscache_calc_len(ractx, fsmap);
+ loff_t pstart = fsmap->m_pa + (fsmap->o_la - fsmap->m_la);
+ int ret;
+
+ ret = erofs_fscache_read_pages(cookie, ractx->mapping,
+ start, length, pstart);
+ if (!ret) {
+ erofs_fscache_unlock_pages(ractx->rac, length);
+ ret = length;
+ }
+
+ return ret;
+}
+
+static int erofs_fscache_ra_inline(struct erofs_fscahce_ra_ctx *ractx,
+ struct erofs_fscache_map *fsmap)
+{
+ struct page *page = readahead_page(ractx->rac);
+ int ret;
+
+ ret = erofs_fscache_readpage_inline(page, fsmap);
+ if (!ret) {
+ SetPageUptodate(page);
+ ret = PAGE_SIZE;
+ }
+
+ unlock_page(page);
+ put_page(page);
+ return ret;
+}
+
+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;
+ struct erofs_fscahce_ra_ctx ractx;
+ int ret;
+
+ if (erofs_inode_is_data_compressed(vi->datalayout)) {
+ erofs_info(sb, "compressed layout not supported yet");
+ return;
+ }
+
+ if (!readahead_count(rac))
+ return;
+
+ ractx = (struct erofs_fscahce_ra_ctx) {
+ .rac = rac,
+ .mapping = rac->mapping,
+ .start = readahead_pos(rac),
+ .len = readahead_length(rac),
+ };
+
+ do {
+ struct erofs_map_blocks map;
+ struct erofs_fscache_map fsmap;
+
+ map.m_la = fsmap.o_la = ractx.start + ractx.done;
+
+ ret = erofs_map_blocks(inode, &map, EROFS_GET_BLOCKS_RAW);
+ if (ret)
+ return;
+
+ if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+ /*
+ * Two cases will hit this:
+ * 1) EOF. Imposibble in readahead routine;
+ * 2) hole. Only CHUNK_BASED layout supports hole.
+ */
+ fsmap.m_la = map.m_la;
+ fsmap.m_llen = map.m_llen;
+ ret = erofs_fscache_ra_hole(&ractx, &fsmap);
+ continue;
+ }
+
+ ret = erofs_fscache_get_map(&fsmap, &map, sb);
+ if (ret)
+ return;
+
+ if (map.m_flags & EROFS_MAP_META) {
+ ret = erofs_fscache_ra_inline(&ractx, &fsmap);
+ continue;
+ }
+
+ switch (vi->datalayout) {
+ case EROFS_INODE_FLAT_PLAIN:
+ case EROFS_INODE_FLAT_INLINE:
+ case EROFS_INODE_CHUNK_BASED:
+ ret = erofs_fscache_ra_noinline(&ractx, &fsmap);
+ break;
+ default:
+ DBG_BUGON(1);
+ return;
+ }
+ } while (ret > 0 && ((ractx.done += ret) < ractx.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,
};

struct page *erofs_fscache_read_cache_page(struct erofs_fscache_context *ctx,
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index f058a04a00c7..2942029a7049 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -616,6 +616,10 @@ 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
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