[pve-devel] [RFC PATCH pve-cluster] fix #5728: pmxcfs: allow bigger writes than 4k for fuse

[Dominik Csapak]

by default libfuse2 limits writes to 4k size, which means that on writes
bigger than that, we do a whole write cycle for each 4k block that comes
in. To avoid that, add the option 'big_writes' to allow writes bigger
than 4k at once.

This should improve pmxcfs performance for situations where we often
write large files (e.g. big ha status) and maybe reduce writes to disk.

If we'd change to libfuse3, this would be a non-issue, since that option
got removed and is the default there.

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
sending as RFC, since I'm not sure if there are maybe any sideeffects i
overlooked. I scanned the pmxcfs code for potential problems where we
would e.g. assume a maximum size of 4096 for fuse writes, but could not
find any. (also my C foo is not that great). I run it here currently,
and it seems to work just fine atm.

 src/pmxcfs/pmxcfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/pmxcfs/pmxcfs.c b/src/pmxcfs/pmxcfs.c
index 1cf8ab8..c5b8f04 100644
--- a/src/pmxcfs/pmxcfs.c
+++ b/src/pmxcfs/pmxcfs.c
@@ -945,7 +945,7 @@ int main(int argc, char *argv[])
 
 	mkdir(CFSDIR, 0755);
 
-	char *fa[] = { "-f", "-odefault_permissions", "-oallow_other", NULL};
+	char *fa[] = { "-f", "-odefault_permissions", "-oallow_other", "-obig_writes", NULL};
 
 	struct fuse_args fuse_args = FUSE_ARGS_INIT(sizeof (fa)/sizeof(gpointer) - 1, fa);
 
-- 
2.39.2