Hi, I didn't originally want to send this proposal because Vlastimil is planning to do some work in this area so I've expected him to send something similar. But the recent discussion about the THP defrag options pushed me to send out my thoughts. So what is the problem? The demand for high order pages is growing and that seems to be the general trend. The problem is that while they can bring performance benefit they can get be really expensive to allocate especially when we enter the direct compaction. So we really want to prevent from expensive path and defer as much as possible to the background. A huge step forward was kcompactd introduced by Vlastimil. We are still not there yet though, because it might be already quite late when we wakeup_kcompactd(). The memory might be already fragmented when we hit there. Moreover we do not have any way to actually tell which orders we do care about. Therefore I believe we need a watermark based pro-active compaction which would keep the background compaction busy as long as we have less pages of the configured order. kcompactd should wake up periodically, I think, and check for the status so that we can catch the fragmentation before we get low on memory. The interface could look something like: /proc/sys/vm/compact_wmark time_period order count There are many details that would have to be solved of course - e.g. do not burn cycles pointlessly when we know that no further progress can be made etc... but in principle the idea show work. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
