[PATCH 6/6] fsverity: kick off hash readahead at data I/O submission time

Christoph Hellwig
2026-01-19T06:23:31Z

Currently all reads of the fsverity hashes is kicked off from the data
I/O completion handler, leading to needlessly dependent I/O. This is
worked around a bit by performing readahead on the level 0 nodes, but
still fairly ineffective.

Switch to a model where the ->read_folio and ->readahead methods instead
kick off explicit readahead of the fsverity hashed so they are usually
available at I/O completion time.

For 64k sequential reads on my test VM this improves read performance
from 2.4GB/s - 2.6GB/s to 3.5GB/s - 3.9GB/s. The improvements for
random reads are likely to be even bigger.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/btrfs/verity.c | 4 +-
fs/ext4/readpage.c | 4 ++
fs/ext4/verity.c | 26 +++++------
fs/f2fs/data.c | 4 ++
fs/f2fs/verity.c | 26 +++++------
fs/verity/read_metadata.c | 10 ++---
fs/verity/verify.c | 92 ++++++++++++++++++++++++++++-----------
include/linux/fsverity.h | 34 ++++++++++++---
8 files changed, 132 insertions(+), 68 deletions(-)

diff --git a/fs/btrfs/verity.c b/fs/btrfs/verity.c
index 8a4426f8b5fb..cd96fac4739f 100644
--- a/fs/btrfs/verity.c
+++ b/fs/btrfs/verity.c
@@ -697,7 +697,6 @@ int btrfs_get_verity_descriptor(struct inode *inode, void *buf, size_t buf_size)
*
* @inode: inode to read a merkle tree page for
* @index: page index relative to the start of the merkle tree
- * @num_ra_pages: number of pages to readahead. Optional, we ignore it
*
* The Merkle tree is stored in the filesystem btree, but its pages are cached
* with a logical position past EOF in the inode's mapping.
@@ -705,8 +704,7 @@ int btrfs_get_verity_descriptor(struct inode *inode, void *buf, size_t buf_size)
* Returns the page we read, or an ERR_PTR on error.
*/
static struct page *btrfs_read_merkle_tree_page(struct inode *inode,
- pgoff_t index,
- unsigned long num_ra_pages)
+ pgoff_t index)
{
struct folio *folio;
u64 off = (u64)index << PAGE_SHIFT;
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index e7f2350c725b..56b3bea657ef 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -226,6 +226,7 @@ int ext4_mpage_readpages(struct inode *inode,
unsigned relative_block = 0;
struct ext4_map_blocks map;
unsigned int nr_pages, folio_pages;
+ unsigned int did_fsverity_readahead = 0;

map.m_pblk = 0;
map.m_lblk = 0;
@@ -241,6 +242,9 @@ int ext4_mpage_readpages(struct inode *inode,
if (rac)
folio = readahead_folio(rac);

+ if (!did_fsverity_readahead++)
+ fsverity_readahead(inode, folio->index, nr_pages);
+
folio_pages = folio_nr_pages(folio);
prefetchw(&folio->flags);

diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
index 2cd6fe2fbf64..baa7277dcf1f 100644
--- a/fs/ext4/verity.c
+++ b/fs/ext4/verity.c
@@ -358,28 +358,25 @@ static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
}

static struct page *ext4_read_merkle_tree_page(struct inode *inode,
- pgoff_t index,
- unsigned long num_ra_pages)
+ pgoff_t index)
{
struct folio *folio;

index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;

- folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
- if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
- DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
-
- if (!IS_ERR(folio))
- folio_put(folio);
- else if (num_ra_pages > 1)
- page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
- folio = read_mapping_folio(inode->i_mapping, index, NULL);
- if (IS_ERR(folio))
- return ERR_CAST(folio);
- }
+ folio = read_mapping_folio(inode->i_mapping, index, NULL);
+ if (IS_ERR(folio))
+ return ERR_CAST(folio);
return folio_file_page(folio, index);
}

+static void ext4_readahead_merkle_tree(struct inode *inode, pgoff_t index,
+ unsigned long nr_pages)
+{
+ index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
+ generic_readahead_merkle_tree(inode, index, nr_pages);
+}
+
static int ext4_write_merkle_tree_block(struct file *file, const void *buf,
u64 pos, unsigned int size)
{
@@ -393,5 +390,6 @@ const struct fsverity_operations ext4_verityops = {
.end_enable_verity = ext4_end_enable_verity,
.get_verity_descriptor = ext4_get_verity_descriptor,
.read_merkle_tree_page = ext4_read_merkle_tree_page,
+ .readahead_merkle_tree = ext4_readahead_merkle_tree,
.write_merkle_tree_block = ext4_write_merkle_tree_block,
};
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index c30e69392a62..c01d5b309751 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2359,6 +2359,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
unsigned nr_pages = rac ? readahead_count(rac) : 1;
unsigned max_nr_pages = nr_pages;
int ret = 0;
+ unsigned int did_fsverity_readahead = 0;

#ifdef CONFIG_F2FS_FS_COMPRESSION
if (f2fs_compressed_file(inode)) {
@@ -2383,6 +2384,9 @@ static int f2fs_mpage_readpages(struct inode *inode,
prefetchw(&folio->flags);
}

+ if (!did_fsverity_readahead++)
+ fsverity_readahead(inode, folio->index, nr_pages);
+
#ifdef CONFIG_F2FS_FS_COMPRESSION
index = folio->index;

diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
index 4326fd72cc72..1ce977937c72 100644
--- a/fs/f2fs/verity.c
+++ b/fs/f2fs/verity.c
@@ -256,28 +256,25 @@ static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
}

static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
- pgoff_t index,
- unsigned long num_ra_pages)
+ pgoff_t index)
{
struct folio *folio;

index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;

- folio = f2fs_filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
- if (IS_ERR(folio) || !folio_test_uptodate(folio)) {
- DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
-
- if (!IS_ERR(folio))
- folio_put(folio);
- else if (num_ra_pages > 1)
- page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
- folio = read_mapping_folio(inode->i_mapping, index, NULL);
- if (IS_ERR(folio))
- return ERR_CAST(folio);
- }
+ folio = read_mapping_folio(inode->i_mapping, index, NULL);
+ if (IS_ERR(folio))
+ return ERR_CAST(folio);
return folio_file_page(folio, index);
}

+static void f2fs_readahead_merkle_tree(struct inode *inode, pgoff_t index,
+ unsigned long nr_pages)
+{
+ index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
+ generic_readahead_merkle_tree(inode, index, nr_pages);
+}
+
static int f2fs_write_merkle_tree_block(struct file *file, const void *buf,
u64 pos, unsigned int size)
{
@@ -291,5 +288,6 @@ const struct fsverity_operations f2fs_verityops = {
.end_enable_verity = f2fs_end_enable_verity,
.get_verity_descriptor = f2fs_get_verity_descriptor,
.read_merkle_tree_page = f2fs_read_merkle_tree_page,
+ .readahead_merkle_tree = f2fs_readahead_merkle_tree,
.write_merkle_tree_block = f2fs_write_merkle_tree_block,
};
diff --git a/fs/verity/read_metadata.c b/fs/verity/read_metadata.c
index cba5d6af4e04..3abaa0a4c40e 100644
--- a/fs/verity/read_metadata.c
+++ b/fs/verity/read_metadata.c
@@ -28,24 +28,24 @@ static int fsverity_read_merkle_tree(struct inode *inode,
if (offset >= end_offset)
return 0;
offs_in_page = offset_in_page(offset);
+ index = offset >> PAGE_SHIFT;
last_index = (end_offset - 1) >> PAGE_SHIFT;

+ __fsverity_readahead(inode, vi, index, last_index - index + 1);
+
/*
* Iterate through each Merkle tree page in the requested range and copy
* the requested portion to userspace. Note that the Merkle tree block
* size isn't important here, as we are returning a byte stream; i.e.,
* we can just work with pages even if the tree block size != PAGE_SIZE.
*/
- for (index = offset >> PAGE_SHIFT; index <= last_index; index++) {
- unsigned long num_ra_pages =
- min_t(unsigned long, last_index - index + 1,
- inode->i_sb->s_bdi->io_pages);
+ for (; index <= last_index; index++) {
unsigned int bytes_to_copy = min_t(u64, end_offset - offset,
PAGE_SIZE - offs_in_page);
struct page *page;
const void *virt;

- page = vops->read_merkle_tree_page(inode, index, num_ra_pages);
+ page = vops->read_merkle_tree_page(inode, index);
if (IS_ERR(page)) {
err = PTR_ERR(page);
fsverity_err(inode,
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
index 3cc81658e4f3..9a96bad82938 100644
--- a/fs/verity/verify.c
+++ b/fs/verity/verify.c
@@ -9,6 +9,7 @@

#include <linux/bio.h>
#include <linux/export.h>
+#include <linux/pagemap.h>

#define FS_VERITY_MAX_PENDING_BLOCKS 2

@@ -21,7 +22,6 @@ struct fsverity_pending_block {
struct fsverity_verification_context {
struct inode *inode;
struct fsverity_info *vi;
- unsigned long max_ra_pages;

/*
* This is the queue of data blocks that are pending verification. When
@@ -37,6 +37,65 @@ struct fsverity_verification_context {

static struct workqueue_struct *fsverity_read_workqueue;

+/**
+ * generic_readahead_merkle_tree() - read ahead from merkle tree
+ * @inode: inode containing fsverity hashes
+ * @index: first data page offset to read ahead for
+ * @nr_pages: number of data pages to read ahead for
+ *
+ * Generic fsverity hashes read implementations for file systems storing
+ * the hashes in the page cache of the data inode. The caller needs to
+ * adjust @index for the fsverity hash offset.
+ */
+void generic_readahead_merkle_tree(struct inode *inode, pgoff_t index,
+ unsigned long nr_pages)
+{
+ struct folio *folio;
+
+ folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);
+ if (PTR_ERR(folio) == -ENOENT || !folio_test_uptodate(folio)) {
+ DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);
+
+ page_cache_ra_unbounded(&ractl, nr_pages, 0);
+ }
+ if (!IS_ERR(folio))
+ folio_put(folio);
+}
+EXPORT_SYMBOL_GPL(generic_readahead_merkle_tree);
+
+void __fsverity_readahead(struct inode *inode, const struct fsverity_info *vi,
+ pgoff_t index, unsigned long nr_pages)
+{
+ const struct merkle_tree_params *params = &vi->tree_params;
+ loff_t data_start_pos = (loff_t)index << PAGE_SHIFT;
+ u64 start_hidx = data_start_pos >> params->log_blocksize;
+ u64 end_hidx = (data_start_pos + ((nr_pages - 1) << PAGE_SHIFT)) >>
+ params->log_blocksize;
+ int level;
+
+ if (!inode->i_sb->s_vop->readahead_merkle_tree)
+ return;
+ if (unlikely(data_start_pos >= inode->i_size))
+ return;
+
+ for (level = 0; level < params->num_levels; level++) {
+ unsigned long level_start = params->level_start[level];
+ unsigned long next_start_hidx = start_hidx >> params->log_arity;
+ unsigned long next_end_hidx = end_hidx >> params->log_arity;
+ unsigned long start_idx = (level_start + next_start_hidx) >>
+ params->log_blocks_per_page;
+ unsigned long end_idx = (level_start + next_end_hidx) >>
+ params->log_blocks_per_page;
+
+ inode->i_sb->s_vop->readahead_merkle_tree(inode, start_idx,
+ end_idx - start_idx + 1);
+
+ start_hidx = next_start_hidx;
+ end_hidx = next_end_hidx;
+ }
+}
+EXPORT_SYMBOL_GPL(__fsverity_readahead);
+
/*
* Returns true if the hash block with index @hblock_idx in the tree, located in
* @hpage, has already been verified.
@@ -114,8 +173,7 @@ static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
* Return: %true if the data block is valid, else %false.
*/
static bool verify_data_block(struct inode *inode, struct fsverity_info *vi,
- const struct fsverity_pending_block *dblock,
- unsigned long max_ra_pages)
+ const struct fsverity_pending_block *dblock)
{
const u64 data_pos = dblock->pos;
const struct merkle_tree_params *params = &vi->tree_params;
@@ -200,8 +258,7 @@ static bool verify_data_block(struct inode *inode, struct fsverity_info *vi,
(params->block_size - 1);

hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode,
- hpage_idx, level == 0 ? min(max_ra_pages,
- params->tree_pages - hpage_idx) : 0);
+ hpage_idx);
if (IS_ERR(hpage)) {
fsverity_err(inode,
"Error %ld reading Merkle tree page %lu",
@@ -272,12 +329,10 @@ static bool verify_data_block(struct inode *inode, struct fsverity_info *vi,

static void
fsverity_init_verification_context(struct fsverity_verification_context *ctx,
- struct inode *inode,
- unsigned long max_ra_pages)
+ struct inode *inode)
{
ctx->inode = inode;
ctx->vi = fsverity_get_info(inode);
- ctx->max_ra_pages = max_ra_pages;
ctx->num_pending = 0;
if (ctx->vi->tree_params.hash_alg->algo_id == HASH_ALGO_SHA256 &&
sha256_finup_2x_is_optimized())
@@ -320,8 +375,7 @@ fsverity_verify_pending_blocks(struct fsverity_verification_context *ctx)
}

for (i = 0; i < ctx->num_pending; i++) {
- if (!verify_data_block(ctx->inode, vi, &ctx->pending_blocks[i],
- ctx->max_ra_pages))
+ if (!verify_data_block(ctx->inode, vi, &ctx->pending_blocks[i]))
return false;
}
fsverity_clear_pending_blocks(ctx);
@@ -371,7 +425,7 @@ bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset)
{
struct fsverity_verification_context ctx;

- fsverity_init_verification_context(&ctx, folio->mapping->host, 0);
+ fsverity_init_verification_context(&ctx, folio->mapping->host);

if (fsverity_add_data_blocks(&ctx, folio, len, offset) &&
fsverity_verify_pending_blocks(&ctx))
@@ -401,22 +455,8 @@ void fsverity_verify_bio(struct bio *bio)
struct inode *inode = bio_first_folio_all(bio)->mapping->host;
struct fsverity_verification_context ctx;
struct folio_iter fi;
- unsigned long max_ra_pages = 0;
-
- if (bio->bi_opf & REQ_RAHEAD) {
- /*
- * If this bio is for data readahead, then we also do readahead
- * of the first (largest) level of the Merkle tree. Namely,
- * when a Merkle tree page is read, we also try to piggy-back on
- * some additional pages -- up to 1/4 the number of data pages.
- *
- * This improves sequential read performance, as it greatly
- * reduces the number of I/O requests made to the Merkle tree.
- */
- max_ra_pages = bio->bi_iter.bi_size >> (PAGE_SHIFT + 2);
- }

- fsverity_init_verification_context(&ctx, inode, max_ra_pages);
+ fsverity_init_verification_context(&ctx, inode);

bio_for_each_folio_all(fi, bio) {
if (!fsverity_add_data_blocks(&ctx, fi.folio, fi.length,
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index deb6b2303d64..84aaa09e07e2 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -90,10 +90,6 @@ struct fsverity_operations {
*
* @inode: the inode
* @index: 0-based index of the page within the Merkle tree
- * @num_ra_pages: The number of Merkle tree pages that should be
- * prefetched starting at @index if the page at @index
- * isn't already cached. Implementations may ignore this
- * argument; it's only a performance optimization.
*
* This can be called at any time on an open verity file. It may be
* called by multiple processes concurrently, even with the same page.
@@ -103,8 +99,10 @@ struct fsverity_operations {
* Return: the page on success, ERR_PTR() on failure
*/
struct page *(*read_merkle_tree_page)(struct inode *inode,
- pgoff_t index,
- unsigned long num_ra_pages);
+ pgoff_t index);
+
+ void (*readahead_merkle_tree)(struct inode *inode, pgoff_t index,
+ unsigned long nr_pages);

/**
* Write a Merkle tree block to the given inode.
@@ -246,4 +244,28 @@ static inline bool fsverity_active(const struct inode *inode)
return fsverity_get_info(inode) != NULL;
}

+/**
+ * fsverity_readahead() - kick off readahead on fsverity hashes
+ * @inode: inode containing fsverity hashes
+ * @index: first data page offset to read ahead for
+ * @nr_pages: number of data pages to read ahead for
+ *
+ * Start readahead on fsverity hashes. To be called from the file systems
+ * ->read_folio and ->readahead methods to ensure that the hashes are
+ * already cached on completion of the file data read if possible.
+ */
+void __fsverity_readahead(struct inode *inode, const struct fsverity_info *vi,
+ pgoff_t index, unsigned long nr_pages);
+static inline void fsverity_readahead(struct inode *inode,
+ pgoff_t index, unsigned long nr_pages)
+{
+ const struct fsverity_info *vi = fsverity_get_info(inode);
+
+ if (vi)
+ __fsverity_readahead(inode, vi, index, nr_pages);
+}
+
+void generic_readahead_merkle_tree(struct inode *inode, pgoff_t index,
+ unsigned long nr_pages);
+
#endif /* _LINUX_FSVERITY_H */
--
2.47.3