[PATCH v6 0/3] Implement readahead for squashfs

[PATCH v6 0/3] Implement readahead for squashfs

[Hsin-Yi Wang]

Commit 9eec1d897139("squashfs: provide backing_dev_info in order to
disable read-ahead") mitigates the performance drop issue for squashfs
by closing readahead for it.

This series implements readahead callback for squashfs. The previous
discussions are in [1] and [2].

[1]
https://lore.kernel.org/all/CAJMQK-g9G6KQmH-V=BRGX0swZji9Wxe_2c7ht-MMAapdFy2pXw@mail.gmail.com/T/
[2]
https://lore.kernel.org/linux-mm/Yn5Yij9pRPCzDozt@casper.infradead.org/t/#m4af4473b94f98a4996cb11756b633a07e5e059d1

This version is based on next-20220610 and the following series:
"Squashfs: handle missing pages decompressing into page cache" [3].

This version is a refresh of ca1505bf4805 ("squashfs: implement
readahead") and 9d58b94aa73a ("squashfs: always build "file direct"
version of page actor").

There's no change in 4af2bd190a5b7 (Revert "squashfs: provide
backing_dev_info in order to disable read-ahead"), but it's carried in
this version too for consistency.

[3]
https://patchwork.kernel.org/project/linux-mm/cover/20220611032133.5743-1-phillip@squashfs.org.uk/

Hsin-Yi Wang (2):
  Revert "squashfs: provide backing_dev_info in order to disable
    read-ahead"
  squashfs: implement readahead

Phillip Lougher (1):
  squashfs: always build "file direct" version of page actor

 fs/squashfs/Makefile     |  4 +-
 fs/squashfs/file.c       | 92 +++++++++++++++++++++++++++++++++++++++-
 fs/squashfs/page_actor.h | 46 --------------------
 fs/squashfs/super.c      | 33 --------------
 4 files changed, 93 insertions(+), 82 deletions(-)

-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v6 1/3] Revert "squashfs: provide backing_dev_info in order to disable read-ahead"

[Hsin-Yi Wang]

This reverts commit 9eec1d897139e5de287af5d559a02b811b844d82.

Revert closing the readahead to squashfs since the readahead callback
for squashfs is implemented.

Suggested-by: Xiongwei Song <Xiongwei.Song@windriver.com>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
---
 fs/squashfs/super.c | 33 ---------------------------------
 1 file changed, 33 deletions(-)

diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index 6d594ba2ed28f..32565dafa7f3b 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -29,7 +29,6 @@
 #include <linux/module.h>
 #include <linux/magic.h>
 #include <linux/xattr.h>
-#include <linux/backing-dev.h>
 
 #include "squashfs_fs.h"
 #include "squashfs_fs_sb.h"
@@ -113,24 +112,6 @@ static const struct squashfs_decompressor *supported_squashfs_filesystem(
 	return decompressor;
 }
 
-static int squashfs_bdi_init(struct super_block *sb)
-{
-	int err;
-	unsigned int major = MAJOR(sb->s_dev);
-	unsigned int minor = MINOR(sb->s_dev);
-
-	bdi_put(sb->s_bdi);
-	sb->s_bdi = &noop_backing_dev_info;
-
-	err = super_setup_bdi_name(sb, "squashfs_%u_%u", major, minor);
-	if (err)
-		return err;
-
-	sb->s_bdi->ra_pages = 0;
-	sb->s_bdi->io_pages = 0;
-
-	return 0;
-}
 
 static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
@@ -146,20 +127,6 @@ static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
 
 	TRACE("Entered squashfs_fill_superblock\n");
 
-	/*
-	 * squashfs provides 'backing_dev_info' in order to disable read-ahead. For
-	 * squashfs, I/O is not deferred, it is done immediately in read_folio,
-	 * which means the user would always have to wait their own I/O. So the effect
-	 * of readahead is very weak for squashfs. squashfs_bdi_init will set
-	 * sb->s_bdi->ra_pages and sb->s_bdi->io_pages to 0 and close readahead for
-	 * squashfs.
-	 */
-	err = squashfs_bdi_init(sb);
-	if (err) {
-		errorf(fc, "squashfs init bdi failed");
-		return err;
-	}
-
 	sb->s_fs_info = kzalloc(sizeof(*msblk), GFP_KERNEL);
 	if (sb->s_fs_info == NULL) {
 		ERROR("Failed to allocate squashfs_sb_info\n");
-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v6 2/3] squashfs: always build "file direct" version of page actor

[Hsin-Yi Wang]

From: Phillip Lougher <phillip@squashfs.org.uk>

Squashfs_readahead uses the "file direct" version of the page
actor, and so build it unconditionally.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
---
v5->v6:
rebase content on top of the dependent series.
---
 fs/squashfs/Makefile     |  4 ++--
 fs/squashfs/page_actor.h | 46 ----------------------------------------
 2 files changed, 2 insertions(+), 48 deletions(-)

diff --git a/fs/squashfs/Makefile b/fs/squashfs/Makefile
index 7bd9b8b856d0b..477c89a519ee8 100644
--- a/fs/squashfs/Makefile
+++ b/fs/squashfs/Makefile
@@ -5,9 +5,9 @@
 
 obj-$(CONFIG_SQUASHFS) += squashfs.o
 squashfs-y += block.o cache.o dir.o export.o file.o fragment.o id.o inode.o
-squashfs-y += namei.o super.o symlink.o decompressor.o
+squashfs-y += namei.o super.o symlink.o decompressor.o page_actor.o
 squashfs-$(CONFIG_SQUASHFS_FILE_CACHE) += file_cache.o
-squashfs-$(CONFIG_SQUASHFS_FILE_DIRECT) += file_direct.o page_actor.o
+squashfs-$(CONFIG_SQUASHFS_FILE_DIRECT) += file_direct.o
 squashfs-$(CONFIG_SQUASHFS_DECOMP_SINGLE) += decompressor_single.o
 squashfs-$(CONFIG_SQUASHFS_DECOMP_MULTI) += decompressor_multi.o
 squashfs-$(CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU) += decompressor_multi_percpu.o
diff --git a/fs/squashfs/page_actor.h b/fs/squashfs/page_actor.h
index 37523c54256fa..24841d28bc0fb 100644
--- a/fs/squashfs/page_actor.h
+++ b/fs/squashfs/page_actor.h
@@ -6,51 +6,6 @@
  * Phillip Lougher <phillip@squashfs.org.uk>
  */
 
-#ifndef CONFIG_SQUASHFS_FILE_DIRECT
-struct squashfs_page_actor {
-	void	**page;
-	int	pages;
-	int	length;
-	int	next_page;
-};
-
-static inline struct squashfs_page_actor *squashfs_page_actor_init(void **page,
-	int pages, int length)
-{
-	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
-
-	if (actor == NULL)
-		return NULL;
-
-	actor->length = length ? : pages * PAGE_SIZE;
-	actor->page = page;
-	actor->pages = pages;
-	actor->next_page = 0;
-	return actor;
-}
-
-static inline void *squashfs_first_page(struct squashfs_page_actor *actor)
-{
-	actor->next_page = 1;
-	return actor->page[0];
-}
-
-static inline void *squashfs_next_page(struct squashfs_page_actor *actor)
-{
-	return actor->next_page == actor->pages ? NULL :
-		actor->page[actor->next_page++];
-}
-
-static inline void squashfs_finish_page(struct squashfs_page_actor *actor)
-{
-	/* empty */
-}
-
-static inline void squashfs_actor_nobuff(struct squashfs_page_actor *actor)
-{
-	/* empty */
-}
-#else
 struct squashfs_page_actor {
 	union {
 		void		**buffer;
@@ -91,4 +46,3 @@ static inline void squashfs_actor_nobuff(struct squashfs_page_actor *actor)
 	actor->alloc_buffer = 0;
 }
 #endif
-#endif
-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v6 3/3] squashfs: implement readahead

[Hsin-Yi Wang]

Implement readahead callback for squashfs. It will read datablocks
which cover pages in readahead request. For a few cases it will
not mark page as uptodate, including:
- file end is 0.
- zero filled blocks.
- current batch of pages isn't in the same datablock.
- decompressor error.
Otherwise pages will be marked as uptodate. The unhandled pages will be
updated by readpage later.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reported-by: Matthew Wilcox <willy@infradead.org>
Reported-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: Xiongwei Song <Xiongwei.Song@windriver.com>
Reported-by: Andrew Morton <akpm@linux-foundation.org>
---
v5->v6:
- use the new squashfs_page_actor_init_special() to handle short file
  cases as well.
- use memzero_page().

v5:
https://lore.kernel.org/lkml/20220606150305.1883410-4-hsinyi@chromium.org/
v4:
https://lore.kernel.org/lkml/20220601103922.1338320-4-hsinyi@chromium.org/
v3:
https://lore.kernel.org/lkml/20220523065909.883444-4-hsinyi@chromium.org/
v2:
https://lore.kernel.org/lkml/20220517082650.2005840-4-hsinyi@chromium.org/
v1:
https://lore.kernel.org/lkml/20220516105100.1412740-3-hsinyi@chromium.org/
---
 fs/squashfs/file.c | 92 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 1 deletion(-)

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index 7f0904b203294..f0c64ee272d5d 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -39,6 +39,7 @@
 #include "squashfs_fs_sb.h"
 #include "squashfs_fs_i.h"
 #include "squashfs.h"
+#include "page_actor.h"
 
 /*
  * Locate cache slot in range [offset, index] for specified inode.  If
@@ -496,7 +497,96 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
 	return res;
 }
 
+static void squashfs_readahead(struct readahead_control *ractl)
+{
+	struct inode *inode = ractl->mapping->host;
+	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
+	size_t mask = (1UL << msblk->block_log) - 1;
+	unsigned short shift = msblk->block_log - PAGE_SHIFT;
+	loff_t start = readahead_pos(ractl) & ~mask;
+	size_t len = readahead_length(ractl) + readahead_pos(ractl) - start;
+	struct squashfs_page_actor *actor;
+	unsigned int nr_pages = 0;
+	struct page **pages;
+	int i, file_end = i_size_read(inode) >> msblk->block_log;
+	unsigned int max_pages = 1UL << shift;
+
+	readahead_expand(ractl, start, (len | mask) + 1);
+
+	if (file_end == 0)
+		return;
+
+	pages = kmalloc_array(max_pages, sizeof(void *), GFP_KERNEL);
+	if (!pages)
+		return;
+
+	for (;;) {
+		pgoff_t index;
+		int res, bsize;
+		u64 block = 0;
+		unsigned int expected;
+
+		nr_pages = __readahead_batch(ractl, pages, max_pages);
+		if (!nr_pages)
+			break;
+
+		if (readahead_pos(ractl) >= i_size_read(inode))
+			goto skip_pages;
+
+		index = pages[0]->index >> shift;
+		if ((pages[nr_pages - 1]->index >> shift) != index)
+			goto skip_pages;
+
+		expected = index == file_end ?
+			   (i_size_read(inode) & (msblk->block_size - 1)) :
+			    msblk->block_size;
+
+		bsize = read_blocklist(inode, index, &block);
+		if (bsize == 0)
+			goto skip_pages;
+
+		actor = squashfs_page_actor_init_special(msblk, pages, nr_pages,
+							 expected);
+		if (!actor)
+			goto skip_pages;
+
+		res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
+
+		kfree(actor);
+
+		if (res == expected) {
+			int bytes;
+
+			/* Last page (if present) may have trailing bytes not filled */
+			bytes = res % PAGE_SIZE;
+			if (pages[nr_pages - 1]->index == file_end && bytes)
+				memzero_page(pages[nr_pages - 1], bytes,
+					     PAGE_SIZE - bytes);
+
+			for (i = 0; i < nr_pages; i++) {
+				flush_dcache_page(pages[i]);
+				SetPageUptodate(pages[i]);
+			}
+		}
+
+		for (i = 0; i < nr_pages; i++) {
+			unlock_page(pages[i]);
+			put_page(pages[i]);
+		}
+	}
+
+	kfree(pages);
+	return;
+
+skip_pages:
+	for (i = 0; i < nr_pages; i++) {
+		unlock_page(pages[i]);
+		put_page(pages[i]);
+	}
+	kfree(pages);
+}
 
 const struct address_space_operations squashfs_aops = {
-	.read_folio = squashfs_read_folio
+	.read_folio = squashfs_read_folio,
+	.readahead = squashfs_readahead
 };
-- 
2.36.1.476.g0c4daa206d-goog

[PATCH 4/3] squashfs: support reading fragments in readahead call

[Phillip Lougher]

This patch adds a function which can be used to read fragments in the
readahead call.

This function is necessary because filesystems built with the -tailends
(or -always-use-fragments) option may have fragments present which
cannot be currently handled.

Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
---
 fs/squashfs/file.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index f0c64ee272d5..3a4cce16d7da 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -497,6 +497,41 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
 	return res;
 }
 
+static unsigned int squashfs_readahead_fragment(struct page **page,
+	unsigned int pages, unsigned int expected)
+{
+	struct inode *inode = page[0]->mapping->host;
+	struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
+		squashfs_i(inode)->fragment_block,
+		squashfs_i(inode)->fragment_size);
+	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
+	unsigned int n, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
+
+	if (buffer->error)
+		goto out;
+
+	expected += squashfs_i(inode)->fragment_offset;
+
+	for (n = 0; n < pages; n++) {
+		unsigned int base = (page[n]->index & mask) << PAGE_SHIFT;
+		unsigned int offset = base + squashfs_i(inode)->fragment_offset;
+
+		if (expected > offset) {
+			unsigned int avail = min_t(unsigned int, expected -
+				offset, PAGE_SIZE);
+
+			squashfs_fill_page(page[n], buffer, offset, avail);
+		}
+
+		unlock_page(page[n]);
+		put_page(page[n]);
+	}
+
+out:
+	squashfs_cache_put(buffer);
+	return buffer->error;
+}
+
 static void squashfs_readahead(struct readahead_control *ractl)
 {
 	struct inode *inode = ractl->mapping->host;
-- 
2.34.1

Re: [PATCH 4/3] squashfs: support reading fragments in readahead call

[Hsin-Yi Wang]

On Fri, Jun 17, 2022 at 11:04 AM Phillip Lougher
<phillip@squashfs.org.uk> wrote:
>
> This patch adds a function which can be used to read fragments in the
> readahead call.
>
> This function is necessary because filesystems built with the -tailends
> (or -always-use-fragments) option may have fragments present which
> cannot be currently handled.
>
> Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
> ---
>  fs/squashfs/file.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
>
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> index f0c64ee272d5..3a4cce16d7da 100644
> --- a/fs/squashfs/file.c
> +++ b/fs/squashfs/file.c
> @@ -497,6 +497,41 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
>         return res;
>  }
>
> +static unsigned int squashfs_readahead_fragment(struct page **page,
hi Phillip,

Since the buffer->error is int, and also the variable to receive the
value is res, I modified it when sending it with the series, though it
won't affect the result.

> +       unsigned int pages, unsigned int expected)
> +{
> +       struct inode *inode = page[0]->mapping->host;
> +       struct squashfs_cache_entry *buffer = squashfs_get_fragment(inode->i_sb,
> +               squashfs_i(inode)->fragment_block,
> +               squashfs_i(inode)->fragment_size);
> +       struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
> +       unsigned int n, mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
> +
> +       if (buffer->error)
> +               goto out;
> +
> +       expected += squashfs_i(inode)->fragment_offset;
> +
> +       for (n = 0; n < pages; n++) {
> +               unsigned int base = (page[n]->index & mask) << PAGE_SHIFT;
> +               unsigned int offset = base + squashfs_i(inode)->fragment_offset;
> +
> +               if (expected > offset) {
> +                       unsigned int avail = min_t(unsigned int, expected -
> +                               offset, PAGE_SIZE);
> +
> +                       squashfs_fill_page(page[n], buffer, offset, avail);
> +               }
> +
> +               unlock_page(page[n]);
> +               put_page(page[n]);
> +       }
> +
> +out:
> +       squashfs_cache_put(buffer);
> +       return buffer->error;
> +}
> +
>  static void squashfs_readahead(struct readahead_control *ractl)
>  {
>         struct inode *inode = ractl->mapping->host;
> --
> 2.34.1
>

Re: [PATCH v6 3/3] squashfs: implement readahead

[Phillip Lougher]

On 13/06/2022 09:28, Hsin-Yi Wang wrote:
> Implement readahead callback for squashfs. It will read datablocks
> which cover pages in readahead request. For a few cases it will
> not mark page as uptodate, including:
> - file end is 0.
> - zero filled blocks.
> - current batch of pages isn't in the same datablock.
> - decompressor error.
> Otherwise pages will be marked as uptodate. The unhandled pages will be
> updated by readpage later.
> 
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
> Reported-by: Matthew Wilcox <willy@infradead.org>
> Reported-by: Phillip Lougher <phillip@squashfs.org.uk>
> Reported-by: Xiongwei Song <Xiongwei.Song@windriver.com>
> Reported-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> v5->v6:
> - use the new squashfs_page_actor_init_special() to handle short file
>    cases as well.

Hi Hsin-Yi,

Thanks for adding the improved page actor support to your patch.

There is currently another problem with the patch, which is it
doesn't handle fragments.

Normally a file (using Mksquashfs defaults) will consist of either:

1. A fragment, stored inside a fragment block, if the file is less
    than the block size, OR

2. One or more datablocks, if the file is greater than the block size.

Your readahead patch handles datablocks, and ignores any file less than
block size by the lines

 > +	if (file_end == 0)
 > +		return;

So in theory the readahead function doesn't have to handle fragments
stored in fragment blocks.

But you can tell Mksquashfs to pack the file tailend into a fragment
block, using the -tailends (or -always-use-fragments) option.

Here, you will get a file which has one or more datablocks, and the last
datablock will be stored in a fragment block.

The readahead code has to handle this, and it is easy to show the code
doesn't by building a filesystem with that option.

I have written a function which can be called to do the work.  This I 
have posted here as a patch.

https://lore.kernel.org/all/20220617030345.24712-1-phillip@squashfs.org.uk/

Obviously, now that fragment blocks are supported, readahead can be
supported for files less than the block size too.

The diff to update the readahead code to use the new function is

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index 1e28fcc22640..aae76de72e2d 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -548,9 +548,6 @@ static void squashfs_readahead(struct 
readahead_control *ractl)

         readahead_expand(ractl, start, (len | mask) + 1);

-       if (file_end == 0)
-               return;
-
         pages = kmalloc_array(max_pages, sizeof(void *), GFP_KERNEL);
         if (!pages)
                 return;
@@ -576,6 +573,14 @@ static void squashfs_readahead(struct 
readahead_control *ractl)
                            (i_size_read(inode) & (msblk->block_size - 1)) :
                             msblk->block_size;

+               if (index == file_end && 
squashfs_i(inode)->fragment_block !=
+                                       SQUASHFS_INVALID_BLK) {
+                       res = squashfs_readahead_fragment(pages, 
nr_pages, expected);
+                       if (res)
+                               goto skip_pages;
+                       continue;
+               }
+
                 bsize = read_blocklist(inode, index, &block);
                 if (bsize == 0)
                         goto skip_pages;
--
2.34.1



> - use memzero_page().
> 
> v5:
> https://lore.kernel.org/lkml/20220606150305.1883410-4-hsinyi@chromium.org/
> v4:
> https://lore.kernel.org/lkml/20220601103922.1338320-4-hsinyi@chromium.org/
> v3:
> https://lore.kernel.org/lkml/20220523065909.883444-4-hsinyi@chromium.org/
> v2:
> https://lore.kernel.org/lkml/20220517082650.2005840-4-hsinyi@chromium.org/
> v1:
> https://lore.kernel.org/lkml/20220516105100.1412740-3-hsinyi@chromium.org/
> ---
>   fs/squashfs/file.c | 92 +++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 91 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
> index 7f0904b203294..f0c64ee272d5d 100644
> --- a/fs/squashfs/file.c
> +++ b/fs/squashfs/file.c
> @@ -39,6 +39,7 @@
>   #include "squashfs_fs_sb.h"
>   #include "squashfs_fs_i.h"
>   #include "squashfs.h"
> +#include "page_actor.h"
>   
>   /*
>    * Locate cache slot in range [offset, index] for specified inode.  If
> @@ -496,7 +497,96 @@ static int squashfs_read_folio(struct file *file, struct folio *folio)
>   	return res;
>   }
>   
> +static void squashfs_readahead(struct readahead_control *ractl)
> +{
> +	struct inode *inode = ractl->mapping->host;
> +	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
> +	size_t mask = (1UL << msblk->block_log) - 1;
> +	unsigned short shift = msblk->block_log - PAGE_SHIFT;
> +	loff_t start = readahead_pos(ractl) & ~mask;
> +	size_t len = readahead_length(ractl) + readahead_pos(ractl) - start;
> +	struct squashfs_page_actor *actor;
> +	unsigned int nr_pages = 0;
> +	struct page **pages;
> +	int i, file_end = i_size_read(inode) >> msblk->block_log;
> +	unsigned int max_pages = 1UL << shift;
> +
> +	readahead_expand(ractl, start, (len | mask) + 1);
> +
> +	if (file_end == 0)
> +		return;
> +
> +	pages = kmalloc_array(max_pages, sizeof(void *), GFP_KERNEL);
> +	if (!pages)
> +		return;
> +
> +	for (;;) {
> +		pgoff_t index;
> +		int res, bsize;
> +		u64 block = 0;
> +		unsigned int expected;
> +
> +		nr_pages = __readahead_batch(ractl, pages, max_pages);
> +		if (!nr_pages)
> +			break;
> +
> +		if (readahead_pos(ractl) >= i_size_read(inode))
> +			goto skip_pages;
> +
> +		index = pages[0]->index >> shift;
> +		if ((pages[nr_pages - 1]->index >> shift) != index)
> +			goto skip_pages;
> +
> +		expected = index == file_end ?
> +			   (i_size_read(inode) & (msblk->block_size - 1)) :
> +			    msblk->block_size;
> +
> +		bsize = read_blocklist(inode, index, &block);
> +		if (bsize == 0)
> +			goto skip_pages;
> +
> +		actor = squashfs_page_actor_init_special(msblk, pages, nr_pages,
> +							 expected);
> +		if (!actor)
> +			goto skip_pages;
> +
> +		res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
> +
> +		kfree(actor);
> +
> +		if (res == expected) {
> +			int bytes;
> +
> +			/* Last page (if present) may have trailing bytes not filled */
> +			bytes = res % PAGE_SIZE;
> +			if (pages[nr_pages - 1]->index == file_end && bytes)
> +				memzero_page(pages[nr_pages - 1], bytes,
> +					     PAGE_SIZE - bytes);
> +
> +			for (i = 0; i < nr_pages; i++) {
> +				flush_dcache_page(pages[i]);
> +				SetPageUptodate(pages[i]);
> +			}
> +		}
> +
> +		for (i = 0; i < nr_pages; i++) {
> +			unlock_page(pages[i]);
> +			put_page(pages[i]);
> +		}
> +	}
> +
> +	kfree(pages);
> +	return;
> +
> +skip_pages:
> +	for (i = 0; i < nr_pages; i++) {
> +		unlock_page(pages[i]);
> +		put_page(pages[i]);
> +	}
> +	kfree(pages);
> +}
>   
>   const struct address_space_operations squashfs_aops = {
> -	.read_folio = squashfs_read_folio
> +	.read_folio = squashfs_read_folio,
> +	.readahead = squashfs_readahead
>   };