On 30.05.19 23:53, Alexander Duyck wrote: > This series provides an asynchronous means of hinting to a hypervisor > that a guest page is no longer in use and can have the data associated > with it dropped. To do this I have implemented functionality that allows > for what I am referring to as "waste page treatment". > > I have based many of the terms and functionality off of waste water > treatment, the idea for the similarity occured to me after I had reached > the point of referring to the hints as "bubbles", as the hints used the > same approach as the balloon functionality but would disappear if they > were touched, as a result I started to think of the virtio device as an > aerator. The general idea with all of this is that the guest should be > treating the unused pages so that when they end up heading "downstream" > to either another guest, or back at the host they will not need to be > written to swap. > > So for a bit of background for the treatment process, it is based on a > sequencing batch reactor (SBR)[1]. The treatment process itself has five > stages. The first stage is the fill, with this we take the raw pages and > add them to the reactor. The second stage is react, in this stage we hand > the pages off to the Virtio Balloon driver to have hints attached to them > and for those hints to be sent to the hypervisor. The third stage is > settle, in this stage we are waiting for the hypervisor to process the > pages, and we should receive an interrupt when it is completed. The fourth > stage is to decant, or drain the reactor of pages. Finally we have the > idle stage which we will go into if the reference count for the reactor > gets down to 0 after a drain, or if a fill operation fails to obtain any > pages and the reference count has hit 0. Otherwise we return to the first > state and start the cycle over again. While I like this analogy, I don't like the terminology mixed into linux-mm core. mm/aeration.c? Bubble? Treated? whut? Can you come up with a terminology once can understand without a PHD in biology? (if that is even the right field of study, I have no idea) ALSO: isn't the analogy partially wrong? Nobody would be using "waste water" just because they are low on "clean water". At least not in my city (I hope so ;) ). But maybe I am not getting the whole concept because we are dealing with pages we want to hint to the hypervisor and not with actual "waste". > > This patch set is still far more intrusive then I would really like for > what it has to do. Currently I am splitting the nr_free_pages into two > values and having to add a pointer and an index to track where we area in > the treatment process for a given free_area. I'm also not sure I have > covered all possible corner cases where pages can get into the free_area > or move from one migratetype to another. Yes, it is quite intrusive. Maybe we can minimize the impact/error proneness. > > Also I am still leaving a number of things hard-coded such as limiting the > lowest order processed to PAGEBLOCK_ORDER, and have left it up to the > guest to determine what size of reactor it wants to allocate to process > the hints. > > Another consideration I am still debating is if I really want to process > the aerator_cycle() function in interrupt context or if I should have it > running in a thread somewhere else. Did you get to test/benchmark the difference? -- Thanks, David / dhildenb
