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SubjectRe: O_DIRECT question
Hua Zhong wrote:
>> The other problem besides the inability to handle IO errors is that
>> mmap()+msync() is synchronous. You need to go async to keep
>> the pipelines full.
> msync(addr, len, MS_ASYNC); doesn't do what you want?

No, because there is no notification of completion. In fact, does this
call actually even avoid blocking in the current code, while asking the
kernel to flush the pages in the background?

Even if it performs the sync in the background, what about faulting in
the pages to be synced? For instance, if you splice pages from a source
mmaped file into the destination mmap, then msync on the destination,
doesn't the process still block to fault in the source pages?

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