My kernel is 2.6.37, I mount a NFS directory on / and found the rsize/wsize=1048576 though "cat /proc/mounts".Now I modify the /etc/fstab to mount the nfs with rsize=2097152, wsize=2097152,but when I remount the NFS,the rsize=1048576,wsize=1048576. the 1048576, 1M , is the max value.
I read the kernel source code, and find the code as below list:

/*
* To change the maximum rsize and wsize supported by the NFS client, adjust
* NFS_MAX_FILE_IO_SIZE. 64KB is a typical maximum, but some servers can
* support a megabyte or more. The default is left at 4096 bytes, which is
* reasonable for NFS over UDP.
*/
#define NFS_MAX_FILE_IO_SIZE (1048576U)
#define NFS_DEF_FILE_IO_SIZE (4096U)
#define NFS_MIN_FILE_IO_SIZE (1024U)

but I modified the NFS_MAX_FILE_IO_SIZE with 2097152, remounted the NFS,the max value was still 1048576. I gussed that kernel source exist some checking code to return to the 1048576.
My question is: how to increase the max value of rsize and wsize?

thank you very much!