[PATCH v7 0/4] Implement readahead for squashfs

[PATCH v7 0/4] 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

v7 adds the patch to support reading fragments in readahead call[3]. No
changes on other patches since v6, which is included in next-20220617.

[3]
https://patchwork.kernel.org/project/linux-mm/patch/20220617030345.24712-1-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 (2):
  squashfs: always build "file direct" version of page actor
  squashfs: support reading fragments in readahead call

 fs/squashfs/Makefile     |   4 +-
 fs/squashfs/file.c       | 133 ++++++++++++++++++++++++++++++++++++++-
 fs/squashfs/page_actor.h |  46 --------------
 fs/squashfs/super.c      |  33 ----------
 4 files changed, 134 insertions(+), 82 deletions(-)

-- 
2.36.1.476.g0c4daa206d-goog

[PATCH v7 1/4] 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 v7 2/4] 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>
---
 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 v7 3/4] 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>
---
 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 v7 4/4] squashfs: support reading fragments in readahead call

[Hsin-Yi Wang]

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

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>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
---
 fs/squashfs/file.c | 47 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index f0c64ee272d5d..98e64fec75b77 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 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;
@@ -513,9 +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;
@@ -541,6 +573,15 @@ 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;
-- 
2.36.1.476.g0c4daa206d-goog

Re: [PATCH v7 0/4] Implement readahead for squashfs

[Phillip Lougher]

On 17/06/2022 09:38, Hsin-Yi Wang wrote:
> 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].

Patch series looks OK to me.

I will be offline at the Glastonbury festival from Tuesday 21 June to
Monday 27 June.

Thanks

Phillip

> 
> [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
> 
> v7 adds the patch to support reading fragments in readahead call[3]. No
> changes on other patches since v6, which is included in next-20220617.
> 
> [3]
> https://patchwork.kernel.org/project/linux-mm/patch/20220617030345.24712-1-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 (2):
>    squashfs: always build "file direct" version of page actor
>    squashfs: support reading fragments in readahead call
> 
>   fs/squashfs/Makefile     |   4 +-
>   fs/squashfs/file.c       | 133 ++++++++++++++++++++++++++++++++++++++-
>   fs/squashfs/page_actor.h |  46 --------------
>   fs/squashfs/super.c      |  33 ----------
>   4 files changed, 134 insertions(+), 82 deletions(-)
>