Re: [RFC PATCH] mm: fadvise: avoid fadvise for fs without backing device

[Shakeel Butt]

>> It doesn't sound like a risky change to me, although perhaps someone is
>> depending on the current behaviour for obscure reasons, who knows.
>>
>> What are the reasons for this change?  Is the current behaviour causing
>> some sort of problem for someone?
>
> Yes, one of our generic library does fadvise(FADV_DONTNEED). Recently
> we observed high latency in fadvise() and notice that the users have
> started using tmpfs files and the latency was due to expensive remote
> LRU cache draining. For normal tmpfs files (have data written on
> them), fadvise(FADV_DONTNEED) will always trigger the un-needed remote
> cache draining.
>

Hi Andrew, do you have more comments or concerns?

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