titan: Fix small blob file can't be gced in fallback mode (#16338)

[ti-chi-bot]

This is an automated cherry-pick of #16338

What is changed and how it works?

Issue Number: Close #16336

What's Changed:

Fix titan small blbo file can't be gced in fallback mode

By the way, change some default values of titan

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• tonyxuqqi
• v01dstar

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[v01dstar]

lgtm

[tonyxuqqi]

/merge

[ti-chi-bot]

@tonyxuqqi: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: b8a1861