Christoph Hellwig <[email protected]> writes: > On Fri, Sep 05, 2014 at 12:09:27PM +0100, Mel Gorman wrote: >> I suggest you look at the recent fincore debate. It did not progress much >> the last time because the author wanted to push a lot of functionality in >> there where as reviewers felt it should start simple. The simple case is >> likely a good fit for what you want. The primary downside is that it would >> be race-prone in memory pressure situations as the page could be reclaimed >> between the fincore check and the read but I expect that your application >> is already avoiding reclaim activity. > > I've actually experimentally hacked up O_NONBLOCK support for regular > files so that it only returns data from the page cache, and not > otherwise. Volker promised to test it with Samba, but we never made > any progress on it, and just last week a customer told me they would > have liked to use it if it was available. > > Note that we might want to also avoid blocking on locks, and I have some > vague memory that we shouldn't actually implement O_NONBLOCK on regular > files due to compatibility options but would have to use a new flag > instead.
FWIW, here's a discussion from an old attempt at O_NONBLOCK for regular files: http://www.gossamer-threads.com/lists/linux/kernel/477936?do=post_view_threaded#477936 I recall it blowing up in various situations, so yeah, a new flag would be a good idea. > Note that mincor/fincore would not help for the usual use case where you > have a non blocking event main loop and want to offload actual blocking > I/O to helper threads, as you it returns information that can be stale > any time. > > One further consideration would be to finally implement real buffered > I/O in kernel space by something like the above and offloading to > workqueues in kernelspace. I think our workqueues now are way better > than any possible user thread pool, although we'd need to find a way to > temporarily tie the work threads to a user address space. Do you mean real buffered AIO? Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
