I read about message integrity using hashing. 

As I know, message integrity is hashing the message content and send to the recipient. If recipient got this message, do hashing again to compare with two hashing value. 

I have one question about that.

May be file size is over 100 MB or something. 

In my opinion, it may take too long. 

So I would like to use some fields such as file size, and creation date in hashing. Is that possible or safe way for hashing?

I recommend the Secure Secure Shell article, which suggests:
ssh-keygen -t ed25519 -a 100

Ed25519 is an EdDSA scheme with very small (fixed size) keys, introduced in OpenSSH 6.5 (2014-01-30) and made default ("first-preference") in OpenSSH 8.5 (2021-03-03).  These have complexity akin to RSA at 4096 bits thanks to elliptic curve cryptography (ECC). The -a 100 option specifies 100 rounds of key derivations, making your key's password harder to brute-force.
However, Ed25519 is a rather new key algorithm (Curve25519's popularity spiked only when it was surmised that other standards had been diluted) and its adoption is not yet universal. Large steps were made in 2018, so we're nearly there, but on older systems or for older servers (like CentOS/RHEL < 7 or Ubuntu < 15.04), you can generate a similarly-complex RSA key with 4096 bits:
ssh-keygen -t rsa -b 4096 -o -a 100

(You may need to omit the -o option since it requires OpenSSH 6.5+ and is the default starting in v7.8, at which point it was removed from the ssh-keygen man page. This dictates usage of a new OpenSSH format to store the key rather than the previous default, PEM. Ed25519 requires this new format, so we do not need to explicitly state it given -t ed25519. A previous man page stated that “the new format has increased resistance to brute-force password cracking.” See this answer for more detail.)
Do not consider the other new ECC algorithm called ECDSA.  It is considered suspect (it has known weaknesses and since the US government has been involved in its development, it may be compromised beyond that). Ed25519 was developed without any known government involvement.
Stay well away from DSA (“ssh-dss”) keys: they're not just suspect, DSA is insecure.
