Re: http://marc.info/?l=linux-mm&m=132732724710038&w=2 (sorry I couldn't properly thread this) > I would like to discuss / brainstorm improvements to > compaction and ways to keep memory allocations better > separated, to be better able to come up with contiguous > 2MB areas. Hi Rik -- I have some thoughts on how in-kernel cleancache/tmem can be used to help achieve this. We can talk about it more in April, but basically: - IMHO the big issue with superpage ballooning is that you need to either maintain a ready-to-use free-list of superpages (but keeping this list is far too wasteful of space); or you need to do just-in-time compaction of a lot of superpages which is time-consuming (periodic "pauses") and subject to failure due to fragmentation. - Under the conditions where you would want to do ballooning, most of the wasted space in a superpage free list would otherwise be used for clean file-mapped pagecache pages. So a large superpage free list would lead to a potentially large increase in refaults (and thus disk reads). So: - Implement a zcache-like driver that allocates 2MB superpages and uses each to store large quantities of cleancache 4K pages (compressed or not) AND all associated meta-data, such that all 4K pages stored in the superpage can be instantly evicted from cleancache simply by removing the superpage from a list. - This list of reclaimable superpages would be primarily used by the balloon superpage driver but can also be reclaimed under certain low-memory conditions. - If implemented properly, there is no internal fragmentation (in the non-compression case). Of course this is not free either; it serves a similar purpose to compaction but amortizes the cost over time. And you have the choice of compression, which increases density by increasing CPU cost, or non-compression which has only page-copy overhead and some small meta-data space overhead. Dan -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href