On Thu, Feb 27, 2014 at 12:03:56PM -0500, Phillip Susi wrote: > > Why build your own cache instead of letting the kernel take care of > it? I believe the IO elevator already gives preferential treatment > to blocking reads so just using readahead() to prefetch and sticking > with plain old read() should work nicely. The reason why it might be better for us to use our own cache is because we can more accurately know when we're done with the block, and we can drop it from the cache. I suppose we could use posix_fadvise(POSIX_FADV_DONTNEED) --- and hopefully this works on block devices for the buffer cache, but it wouldn't all surprise me that if we can get finer-grained control if we use O_DIRECT and manage the buffers ourselves. Whether it's worth the extra complexitry is a fair question --- but simply adding metadata prefetching is going to add a fair amount of complexity already, and we should test to make sure that readahead() and posix_fadvise() actually work correctly on block devices --- a couple of years ago, I had explored readahead() precisely as a cheap way of adding metadata precaching for e2fsck, and it was a no-op when I tried the test back then. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
