On Thu, Mar 26, 2015 at 08:28:24PM -0700, Andrew Morton wrote: > A thing which bugs me about pread2() is that it is specifically > tailored to applications which are able to use a partial read result. > ie, by sending it over the network. Can you explain what you mean by this? Samba gets a pread request from a client for some bytes. The client will be confused when we send less than requested although the file is long enough to satisfy all. > And of course fincore could be used by Samba etc to avoid blocking on > reads. It wouldn't perform quite as well as pread2(), but I bet it's > good enough. > > Bottom line: with pread2() there's still a need for fincore(), but with > fincore() there probably isn't a need for pread2(). fincore would be a second syscall per pread, and it is not atomic. I've had discussions with MIPS based vendors who are worried about every single syscall. This is the #1 hottest code path in Samba. > And I'm doubtful about claims that it absolutely has to be non-blocking > 100% of the time. I bet that 99.99% is good enough. A fincore() > option to run mark_page_accessed() against present pages would help > with the race-with-reclaim situation. If you can make sure that after an fincore the pages remain in memory for x milliseconds the atomicity concern might go away. 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
