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, 6 insertions, 1 deletions

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 31a504f1ee60..76f46f159992 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -120,6 +120,7 @@
  *  7.28
  *  - add FUSE_COPY_FILE_RANGE
  *  - add FOPEN_CACHE_DIR
+ *  - add FUSE_MAX_PAGES, add max_pages to init_out
  */
 
 #ifndef _LINUX_FUSE_H
@@ -255,6 +256,7 @@ struct fuse_file_lock {
  * FUSE_HANDLE_KILLPRIV: fs handles killing suid/sgid/cap on write/chown/trunc
  * FUSE_POSIX_ACL: filesystem supports posix acls
  * FUSE_ABORT_ERROR: reading the device after abort returns ECONNABORTED
+ * FUSE_MAX_PAGES: init_out.max_pages contains the max number of req pages
  */
 #define FUSE_ASYNC_READ         (1 << 0)
 #define FUSE_POSIX_LOCKS        (1 << 1)
@@ -278,6 +280,7 @@ struct fuse_file_lock {
 #define FUSE_HANDLE_KILLPRIV    (1 << 19)
 #define FUSE_POSIX_ACL          (1 << 20)
 #define FUSE_ABORT_ERROR        (1 << 21)
+#define FUSE_MAX_PAGES          (1 << 22)
 
 /**
  * CUSE INIT request/reply flags
@@ -617,7 +620,9 @@ struct fuse_init_out {
         uint16_t        congestion_threshold;
         uint32_t        max_write;
         uint32_t        time_gran;
-        uint32_t        unused[9];
+        uint16_t        max_pages;
+        uint16_t        padding;
+        uint32_t        unused[8];
 };
 
 #define CUSE_INIT_INFO_MAX 4096