fuse: add max_pages to init_out

Replace FUSE_MAX_PAGES_PER_REQ with the configurable parameter max_pages to
improve performance.

Old RFC with detailed description of the problem and many fixes by Mitsuo
Hayasaka (mitsuo.hayasaka.hu@hitachi.com):
 - https://lkml.org/lkml/2012/7/5/136

We've encountered performance degradation and fixed it on a big and complex
virtual environment.

Environment to reproduce degradation and improvement:

1. Add lag to user mode FUSE
Add nanosleep(&(struct timespec){ 0, 1000 }, NULL); to xmp_write_buf in
passthrough_fh.c

2. patch UM fuse with configurable max_pages parameter. The patch will be
provided latter.

3. run test script and perform test on tmpfs
fuse_test()
{

       cd /tmp
       mkdir -p fusemnt
       passthrough_fh -o max_pages=$1 /tmp/fusemnt
       grep fuse /proc/self/mounts
       dd conv=fdatasync oflag=dsync if=/dev/zero of=fusemnt/tmp/tmp \
		count=1K bs=1M 2>&1 | grep -v records
       rm fusemnt/tmp/tmp
       killall passthrough_fh
}

Test results:

passthrough_fh /tmp/fusemnt fuse.passthrough_fh \
	rw,nosuid,nodev,relatime,user_id=0,group_id=0 0 0
1073741824 bytes (1.1 GB) copied, 1.73867 s, 618 MB/s

passthrough_fh /tmp/fusemnt fuse.passthrough_fh \
	rw,nosuid,nodev,relatime,user_id=0,group_id=0,max_pages=256 0 0
1073741824 bytes (1.1 GB) copied, 1.15643 s, 928 MB/s

Obviously with bigger lag the difference between 'before' and 'after'
will be more significant.

Mitsuo Hayasaka, in 2012 (https://lkml.org/lkml/2012/7/5/136),
observed improvement from 400-550 to 520-740.

Signed-off-by: Constantine Shulyupin <const@MakeLinux.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index f5bdce84e766..3d578745c852 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -28,8 +28,11 @@
 #include <linux/refcount.h>
 #include <linux/user_namespace.h>
 
-/** Max number of pages that can be used in a single read request */
-#define FUSE_MAX_PAGES_PER_REQ 32
+/** Default max number of pages that can be used in a single read request */
+#define FUSE_DEFAULT_MAX_PAGES_PER_REQ 32
+
+/** Maximum of max_pages received in init_out */
+#define FUSE_MAX_MAX_PAGES 256
 
 /** Bias for fi->writectr, meaning new writepages must not be sent */
 #define FUSE_NOWRITE INT_MIN
@@ -525,6 +528,9 @@ struct fuse_conn {
 	/** Maximum write size */
 	unsigned max_write;
 
+	/** Maxmum number of pages that can be used in a single request */
+	unsigned int max_pages;
+
 	/** Input queue */
 	struct fuse_iqueue iq;