Re: zeroed pages in pread result

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On Tue, Apr 10, 2018 at 06:54:58PM +0000, Sage Weil wrote:
> The one other curious thing is that we tried doing a memset on the buffer 
> with a non-zero value before the read to see whether pread was skipping 
> the pages or filling them with zeros...and weren't able to reproduce the 
> failure.  It's a bit hard to trigger at baseline (it takes anywhere from 
> hours to days) so we may not have waited long enough.  We're kicking off 
> another run with memset to try again.
> 
> Any theories or suggestions?

That makes me wonder if the user pages were paged out, and there's some
kind of bug getting those pages back into memory ...

I assume you're reading into anonymous memory and not something weird
like device memory.  But maybe you're reading into a MAP_SHARED of a file?



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