[RFC PATCH 3/5] fuse: make default global limit minimum value

[Mitsuo Hayasaka]

The default global limits for congestion threshold and backgrounded
requests are calculated using size of fuse_req structure, which is
variable due to the tunable read/write request size. This patch sets
them to their minimum values by default in order to avoid the variable
and unstable limits per mount.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@xxxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
---

 fs/fuse/fuse_i.h |    5 +++++
 fs/fuse/inode.c  |    2 +-
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index c96dc5f..72210a8 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -29,6 +29,11 @@
 /** Default number of pages that can be used in a single read/write request */
 #define FUSE_DEFAULT_MAX_PAGES_PER_REQ 32
 
+/** Maximum size of struct fuse_req */
+#define FUSE_MAX_FUSE_REQ_SIZE	(sizeof(struct fuse_req) + \
+				 FUSE_MAX_PAGES_PER_REQ * \
+				 sizeof(struct page *))
+
 /** Bias for fi->writectr, meaning new writepages must not be sent */
 #define FUSE_NOWRITE INT_MIN
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index aadf157..d8d302a 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -758,7 +758,7 @@ static void sanitize_global_limit(unsigned *limit)
 {
 	if (*limit == 0)
 		*limit = ((num_physpages << PAGE_SHIFT) >> 13) /
-			 sizeof(struct fuse_req);
+			 FUSE_MAX_FUSE_REQ_SIZE;
 
 	if (*limit >= 1 << 16)
 		*limit = (1 << 16) - 1;

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