On Fri, Mar 27, 2015 at 02:01:59AM -0700, Andrew Morton wrote: > 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. Sorry, but I don't have a good picture how we are supposed to use that. I'm fine with two syscalls, but I need a way to tell the kernel to either block or not. Or do you want Samba to do repeated pread calls for ever shorter blocks? Right now I don't see a way to tell pread to either give me a short result or really block. To me that's the core of preadv2. I'm perfectly find for a syscall to give me a short read instead of a global EWOULDBLOCK. I need a way to tell the kernel which behaviour I want. Volker -- SerNet GmbH, Bahnhofsallee 1b, 37081 Göttingen phone: +49-551-370000-0, fax: +49-551-370000-9 AG Göttingen, HRB 2816, GF: Dr. Johannes Loxen http://www.sernet.de, mailto:kontakt@xxxxxxxxx -- 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
