Re: [PATCH v7 0/5] vfs: Non-blockling buffered fs read (page cache only)

On Fri, Mar 27, 2015 at 09:02:51AM +0100, Volker Lendecke wrote:

No, this is not the case. Maybe my whole understanding of
pread is wrong: I always thought that it won't return short
if the file spans the pread range. EINTR nonwithstanding.

Per Posix it could, however if we do it for regular file reads
hell will break lose because no one expects it.  So in practice
it can't.

quoted

	if (it's all in cache)

I know I'm repeating myself: We have a race condition here.
A small one, but it is racy. I've seen loaded systems where
we spend seconds between becoming re-scheduled. In these
systems, it will be the norm to block in later reads. And we
don't have a good way to detect this situation afterwards
and turn to threads as a precaution next time.

Exactly.  One that matters in real life, too.  Nevermind that
preadv2 is a way cleaner interface than fincore.