On Tue, Feb 14, 2012 at 01:33:37PM -0800, Andrew Morton wrote: > On Sun, 12 Feb 2012 01:21:35 +0100 > Andrea Righi <andrea@xxxxxxxxxxxxxxx> wrote: > > > The new proposal is to implement POSIX_FADV_NOREUSE as a way to perform a real > > drop-behind policy where applications can mark certain intervals of a file as > > FADV_NOREUSE before accessing the data. > > I think you and John need to talk to each other, please. The amount of > duplication here is extraordinary. Yes, definitely. I'm currently reviewing and testing the John's patch set. I was even considering to apply my patch set on top of the John's patch, or at least propose my tree-based approach to manage the list of the POSIX_FADV_VOLATILE ranges. > > Both patchsets add fields to the address_space (and hence inode), which > is significant - we should convince ourselves that we're getting really > good returns from a feature which does this. > > > > Regarding the use of fadvise(): I suppose it's a reasonable thing to do > in the long term - if the feature works well, popular data streaming > applications will eventually switch over. But I do think we should > explore interfaces which don't require modification of userspace source > code. Because there will always be unconverted applications, and the > feature becomes available immediately. > > One such interface would be to toss the offending application into a > container which has a modified drop-behind policy. And here we need to > drag out the crystal ball: what *is* the best way of tuning application > pagecache behaviour? Will we gravitate towards containerization, or > will we gravitate towards finer-tuned fadvise/sync_page_range/etc > behaviour? Thus far it has been the latter, and I don't think that has > been a great success. > > Finally, are the problems which prompted these patchsets already > solved? What happens if you take the offending streaming application > and toss it into a 16MB memcg? That *should* avoid perturbing other > things running on that machine. Moving the streaming application into a 16MB memcg can be dangerous in some cases... the application might start to do "bad" things, like swapping (if the memcg can swap) or just fail due to OOMs. > > And yes, a container-based approach is pretty crude, and one can > envision applications which only want modified reclaim policy for one > particualr file. But I suspect an application-wide reclaim policy > solves 90% of the problems. I really like the container-based approach. But for this we need a better file cache control in the memory cgroup; now we have the accounting of file pages, but there's no way to limit them. Thanks for your comments, Andrew. -Andrea -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
