What the differences between "__GFP_NOFAIL" and "__GFP_REPEAT"?

[孙世龙 sunshilong]

As per the documentation( https://www.linuxjournal.com/article/6930),
which says:
    Flag                Description
__GFP_REPEAT   The kernel repeats the allocation if it fails.
__GFP_NOFAIL   The kernel can repeat the allocation.

So, both of them may cause the kernel to repeat the allocation operation.
How can I choose between them?
What are the major differences?

Thank you for your attention to this matter.
Looking forward to hearing from you.
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