On Fri, 27 Mar 2015 01:48:33 -0700 Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Fri, Mar 27, 2015 at 01:35:16AM -0700, Andrew Morton wrote: > > fincore() doesn't have to be ugly. Please address the design issues I > > raised. How is pread2() useful to the class of applications which > > cannot proceed until all data is available? > > It actually makes them work correctly? preadv2( ..., DONTWAIT) will > return -EGAIN, which causes them to bounce to the threadpool where > they call preadv(...). (I assume you mean RWF_NONBLOCK) That isn't how pread2() works. If the leading one or more pages are uptodate, pread2() will return a partial read. Now what? Either the application reads the same data a second time via the worker thread (dumb, but it will usually be a rare case) or it reads the remainder of the data in the worker thread and splices the data back together. Which, as I said, will often result in a second load of the initial read result into CPU cache. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
