Date:	Fri, 11 Oct 2013 07:19:40 +0100
From:	Phillip Lougher <phillip@...ashfs.org.uk>
To:	linux-kernel@...r.kernel.org
Cc:	minchan@...nel.org, Phillip Lougher <phillip@...ashfs.org.uk>
Subject: [PATCH 3/3] Squashfs: Directly decompress into the page cache for file data

This introduces an implementation of squashfs_readpage_block()
that directly decompresses into the page cache.

This uses the previously added page handler abstraction to push
down the necessary kmap_atomic/kunmap_atomic operations on the
page cache buffers into the decompressors.  This enables
direct copying into the page cache without using the slow
kmap/kunmap calls.

The code detects when multiple threads are racing in
squashfs_readpage() to decompress the same block, and avoids
this regression by falling back to using an intermediate
buffer.

This patch enhances the performance of Squashfs significantly
when multiple processes are accessing the filesystem simultaneously
because it not only reduces memcopying, but it more importantly
eliminates the lock contention on the intermediate buffer.

Using single-thread decompression.

        dd if=file1 of=/dev/null bs=4096 &
        dd if=file2 of=/dev/null bs=4096 &
        dd if=file3 of=/dev/null bs=4096 &
        dd if=file4 of=/dev/null bs=4096

Before:

629145600 bytes (629 MB) copied, 45.8046 s, 13.7 MB/s

After:

629145600 bytes (629 MB) copied, 9.29414 s, 67.7 MB/s

Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
---
 fs/squashfs/Kconfig       |  14 ++++
 fs/squashfs/Makefile      |   7 +-
 fs/squashfs/file_direct.c | 178 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/squashfs/page_actor.c  | 104 +++++++++++++++++++++++++++
 fs/squashfs/page_actor.h  |  32 +++++++++
 5 files changed, 334 insertions(+), 1 deletion(-)
 create mode 100644 fs/squashfs/file_direct.c
 create mode 100644 fs/squashfs/page_actor.c

diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
index c70111e..8bc9e6a 100644
--- a/fs/squashfs/Kconfig
+++ b/fs/squashfs/Kconfig
@@ -25,6 +25,20 @@ config SQUASHFS
 
 	  If unsure, say N.
 
+config SQUASHFS_FILE_DIRECT
+	bool "Decompress files directly into the page cache"
+	depends on SQUASHFS
+	help
+	  Squashfs has traditionally decompressed file data into an
+	  intermediate buffer and then memcopied it into the page cache.
+
+	  Saying Y here includes support for directly decompressing
+	  file data into the page cache.  Doing so can significantly
+	  improve performance because it eliminates a mempcpy and
+	  it also removes the lock contention on the single buffer.
+
+	  If unsure, say N.
+
 config SQUASHFS_XATTR
 	bool "Squashfs XATTR support"
 	depends on SQUASHFS
diff --git a/fs/squashfs/Makefile b/fs/squashfs/Makefile
index 14cfc41..deaabc5 100644
--- a/fs/squashfs/Makefile
+++ b/fs/squashfs/Makefile
@@ -5,8 +5,13 @@
 obj-$(CONFIG_SQUASHFS) += squashfs.o
 squashfs-y += block.o cache.o dir.o export.o file.o fragment.o id.o inode.o
 squashfs-y += namei.o super.o symlink.o decompressor.o decompressor_single.o
-squashfs-y += file_cache.o
 squashfs-$(CONFIG_SQUASHFS_XATTR) += xattr.o xattr_id.o
 squashfs-$(CONFIG_SQUASHFS_LZO) += lzo_wrapper.o
 squashfs-$(CONFIG_SQUASHFS_XZ) += xz_wrapper.o
 squashfs-$(CONFIG_SQUASHFS_ZLIB) += zlib_wrapper.o
+
+ifdef CONFIG_SQUASHFS_FILE_DIRECT
+    squashfs-y += file_direct.o page_actor.o
+else
+    squashfs-y += file_cache.o
+endif
diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
new file mode 100644
index 0000000..f31298e
--- /dev/null
+++ b/fs/squashfs/file_direct.c
@@ -0,0 +1,178 @@
+/*
+ * Copyright (c) 2013
+ * Phillip Lougher <phillip@...ashfs.org.uk>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ */
+
+#include <linux/fs.h>
+#include <linux/vfs.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/pagemap.h>
+#include <linux/mutex.h>
+
+#include "squashfs_fs.h"
+#include "squashfs_fs_sb.h"
+#include "squashfs_fs_i.h"
+#include "squashfs.h"
+#include "page_actor.h"
+
+static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
+	int pages, struct page **page);
+
+/* Read separately compressed datablock directly into page cache */
+int squashfs_readpage_block(struct page *target_page, u64 block, int bsize)
+
+{
+	struct inode *inode = target_page->mapping->host;
+	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
+
+	int file_end = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;
+	int mask = (1 << (msblk->block_log - PAGE_CACHE_SHIFT)) - 1;
+	int start_index = target_page->index & ~mask;
+	int end_index = start_index | mask;
+	int i, n, pages, missing_pages, bytes, res = -ENOMEM;
+	struct page **page;
+	struct squashfs_page_actor *actor;
+	void *pageaddr;
+
+	if (end_index > file_end)
+		end_index = file_end;
+
+	pages = end_index - start_index + 1;
+
+	page = kmalloc(sizeof(void *) * pages, GFP_KERNEL);
+	if (page == NULL)
+		goto error_out;
+
+	/*
+	 * Create a "page actor" which will kmap and kunmap the
+	 * page cache pages appropriately within the decompressor
+	 */
+	actor = squashfs_page_actor_init_special(page, pages, 0);
+	if (actor == NULL)
+		goto error_out2;
+
+	/* Try to grab all the pages covered by the Squashfs block */
+	for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
+		page[i] = (n == target_page->index) ? target_page :
+			grab_cache_page_nowait(target_page->mapping, n);
+
+		if (page[i] == NULL) {
+			missing_pages++;
+			continue;
+		}
+
+		if (PageUptodate(page[i])) {
+			unlock_page(page[i]);
+			page_cache_release(page[i]);
+			page[i] = NULL;
+			missing_pages++;
+		}
+	}
+
+	if (missing_pages) {
+		/*
+		 * Couldn't get one or more pages - probably because we're
+		 * racing with another thread in squashfs_readpage also
+		 * trying to grab them.  Fall back to using an intermediate
+		 * buffer.  Note as this page conflict is mutual, we
+		 * know all the racing processes will do this.
+		 */
+		kfree(actor);
+		return squashfs_read_cache(target_page, block, bsize, pages,
+								page);
+	}
+
+	/* Decompress directly into the page cache buffers */
+	res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
+	if (res < 0)
+		goto mark_errored;
+
+	/* Last page may have trailing bytes not filled */
+	bytes = res % PAGE_CACHE_SIZE;
+	if (bytes) {
+		pageaddr = kmap_atomic(page[pages - 1]);
+		memset(pageaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);
+		kunmap_atomic(pageaddr);
+	}
+
+	/* Mark pages as uptodate, unlock and release */
+	for (i = 0; i < pages; i++) {
+		flush_dcache_page(page[i]);
+		SetPageUptodate(page[i]);
+		unlock_page(page[i]);
+		if (page[i] != target_page)
+			page_cache_release(page[i]);
+	}
+
+	kfree(actor);
+	kfree(page);
+
+	return 0;
+
+mark_errored:
+	/* Decompression failed, mark pages as errored.  Target_page is
+	 * dealt with by the caller
+	 */
+	for (i = 0; i < pages; i++) {
+		if (page[i] == target_page)
+			continue;
+		pageaddr = kmap_atomic(page[i]);
+		memset(pageaddr, 0, PAGE_CACHE_SIZE);
+		kunmap_atomic(pageaddr);
+		flush_dcache_page(page[i]);
+		SetPageError(page[i]);
+		unlock_page(page[i]);
+		page_cache_release(page[i]);
+	}
+
+	kfree(actor);
+error_out2:
+	kfree(page);
+error_out:
+	return res;
+}
+
+
+static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
+	int pages, struct page **page)
+{
+	struct inode *i = target_page->mapping->host;
+	struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
+						 block, bsize);
+	int bytes = buffer->length, res = buffer->error, n, offset = 0;
+	void *pageaddr;
+
+	if (res) {
+		ERROR("Unable to read page, block %llx, size %x\n", block,
+			bsize);
+		goto out;
+	}
+
+	for (n = 0; n < pages && bytes > 0; n++,
+			bytes -= PAGE_CACHE_SIZE, offset += PAGE_CACHE_SIZE) {
+		int avail = min_t(int, bytes, PAGE_CACHE_SIZE);
+
+		if (page[n] == NULL)
+			continue;
+
+		pageaddr = kmap_atomic(page[n]);
+		squashfs_copy_data(pageaddr, buffer, offset, avail);
+		memset(pageaddr + avail, 0, PAGE_CACHE_SIZE - avail);
+		kunmap_atomic(pageaddr);
+		flush_dcache_page(page[n]);
+		SetPageUptodate(page[n]);
+		unlock_page(page[n]);
+		if (page[n] != target_page)
+			page_cache_release(page[n]);
+	}
+
+out:
+	squashfs_cache_put(buffer);
+	kfree(page);
+	return res;
+}
diff --git a/fs/squashfs/page_actor.c b/fs/squashfs/page_actor.c
new file mode 100644
index 0000000..8e754ff
--- /dev/null
+++ b/fs/squashfs/page_actor.c
@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2013
+ * Phillip Lougher <phillip@...ashfs.org.uk>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2. See
+ * the COPYING file in the top-level directory.
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/pagemap.h>
+#include "page_actor.h"
+
+/* Implementation of page_actor for decompressing into intermediate buffer */
+static void *cache_first_page(struct squashfs_page_actor *actor)
+{
+	actor->next_page = 1;
+	return actor->buffer[0];
+}
+
+static void *cache_next_page(struct squashfs_page_actor *actor)
+{
+	if (actor->next_page == actor->pages)
+		return NULL;
+
+	return actor->buffer[actor->next_page++];
+}
+
+static void cache_finish_page(struct squashfs_page_actor *actor)
+{
+	/* empty */
+}
+
+struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
+	int pages, int length)
+{
+	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
+
+	if (actor == NULL)
+		return NULL;
+
+	if (length)
+		actor->length = length;
+	else
+		actor->length = pages * PAGE_CACHE_SIZE;
+	actor->buffer = buffer;
+	actor->pages = pages;
+	actor->next_page = 0;
+
+	actor->squashfs_first_page = cache_first_page;
+	actor->squashfs_next_page = cache_next_page;
+	actor->squashfs_finish_page = cache_finish_page;
+	return actor;
+}
+
+/* Implementation of page_actor for decompressing directly into page cache */
+static void *direct_first_page(struct squashfs_page_actor *actor)
+{
+	actor->next_page = 1;
+	return actor->pageaddr = kmap_atomic(actor->page[0]);
+}
+
+static void *direct_next_page(struct squashfs_page_actor *actor)
+{
+	if (actor->pageaddr)
+		kunmap_atomic(actor->pageaddr);
+
+	if (actor->next_page == actor->pages) {
+		actor->pageaddr = NULL;
+		return NULL;
+	}
+
+	return actor->pageaddr = kmap_atomic(actor->page[actor->next_page++]);
+}
+
+static void direct_finish_page(struct squashfs_page_actor *actor)
+{
+	if (actor->pageaddr)
+		kunmap_atomic(actor->pageaddr);
+}
+
+
+struct squashfs_page_actor *squashfs_page_actor_init_special(struct page **page,
+	int pages, int length)
+{
+	struct squashfs_page_actor *actor = kmalloc(sizeof(*actor), GFP_KERNEL);
+
+	if (actor == NULL)
+		return NULL;
+
+	if (length)
+		actor->length = length;
+	else
+		actor->length = pages * PAGE_CACHE_SIZE;
+	actor->page = page;
+	actor->pages = pages;
+	actor->next_page = 0;
+	actor->pageaddr = NULL;
+
+	actor->squashfs_first_page = direct_first_page;
+	actor->squashfs_next_page = direct_next_page;
+	actor->squashfs_finish_page = direct_finish_page;
+	return actor;
+}
diff --git a/fs/squashfs/page_actor.h b/fs/squashfs/page_actor.h
index 19a66a3..22731c7 100644
--- a/fs/squashfs/page_actor.h
+++ b/fs/squashfs/page_actor.h
@@ -8,6 +8,7 @@
  * the COPYING file in the top-level directory.
  */
 
+#ifndef CONFIG_SQUASHFS_FILE_DIRECT
 struct squashfs_page_actor {
 	void	**page;
 	int	pages;
@@ -51,4 +52,35 @@ static inline void squashfs_finish_page(struct squashfs_page_actor *actor)
 {
 	/* empty */
 }
+#else
+struct squashfs_page_actor {
+	union {
+		void		**buffer;
+		struct page	**page;
+	};
+	void	*pageaddr;
+	void    *(*squashfs_first_page)(struct squashfs_page_actor *);
+	void    *(*squashfs_next_page)(struct squashfs_page_actor *);
+	void    (*squashfs_finish_page)(struct squashfs_page_actor *);
+	int	pages;
+	int	length;
+	int	next_page;
+};
+
+extern struct squashfs_page_actor *squashfs_page_actor_init(void **, int, int);
+extern struct squashfs_page_actor *squashfs_page_actor_init_special(struct page
+							 **, int, int);
+static inline void *squashfs_first_page(struct squashfs_page_actor *actor)
+{
+	return actor->squashfs_first_page(actor);
+}
+static inline void *squashfs_next_page(struct squashfs_page_actor *actor)
+{
+	return actor->squashfs_next_page(actor);
+}
+static inline void squashfs_finish_page(struct squashfs_page_actor *actor)
+{
+	actor->squashfs_finish_page(actor);
+}
+#endif
 #endif
-- 
1.8.3.2

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