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. 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. 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. -- 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
