[Cc linux-api] On Tue 21-05-19 13:39:50, Minchan Kim wrote: > On Mon, May 20, 2019 at 12:46:05PM -0400, Johannes Weiner wrote: > > On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote: > > > - Approach > > > > > > The approach we chose was to use a new interface to allow userspace to > > > proactively reclaim entire processes by leveraging platform information. > > > This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages > > > that are known to be cold from userspace and to avoid races with lmkd > > > by reclaiming apps as soon as they entered the cached state. Additionally, > > > it could provide many chances for platform to use much information to > > > optimize memory efficiency. > > > > > > IMHO we should spell it out that this patchset complements MADV_WONTNEED > > > and MADV_FREE by adding non-destructive ways to gain some free memory > > > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the > > > kernel that memory region is not currently needed and should be reclaimed > > > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the > > > kernel that memory region is not currently needed and should be reclaimed > > > when memory pressure rises. > > > > I agree with this approach and the semantics. But these names are very > > vague and extremely easy to confuse since they're so similar. > > > > MADV_COLD could be a good name, but for deactivating pages, not > > reclaiming them - marking memory "cold" on the LRU for later reclaim. > > > > For the immediate reclaim one, I think there is a better option too: > > In virtual memory speak, putting a page into secondary storage (or > > ensuring it's already there), and then freeing its in-memory copy, is > > called "paging out". And that's what this flag is supposed to do. So > > how about MADV_PAGEOUT? > > > > With that, we'd have: > > > > MADV_FREE: Mark data invalid, free memory when needed > > MADV_DONTNEED: Mark data invalid, free memory immediately > > > > MADV_COLD: Data is not used for a while, free memory when needed > > MADV_PAGEOUT: Data is not used for a while, free memory immediately > > > > What do you think? > > There are several suggestions until now. Thanks, Folks! > > For deactivating: > > - MADV_COOL > - MADV_RECLAIM_LAZY > - MADV_DEACTIVATE > - MADV_COLD > - MADV_FREE_PRESERVE > > > For reclaiming: > > - MADV_COLD > - MADV_RECLAIM_NOW > - MADV_RECLAIMING > - MADV_PAGEOUT > - MADV_DONTNEED_PRESERVE > > It seems everybody doesn't like MADV_COLD so want to go with other. > For consisteny of view with other existing hints of madvise, -preserve > postfix suits well. However, originally, I don't like the naming FREE > vs DONTNEED from the beginning. They were easily confused. > I prefer PAGEOUT to RECLAIM since it's more likely to be nuance to > represent reclaim with memory pressure and is supposed to paged-in > if someone need it later. So, it imply PRESERVE. > If there is not strong against it, I want to go with MADV_COLD and > MADV_PAGEOUT. > > Other opinion? I do not really care strongly. I am pretty sure we will have a lot of suggestions because people tend to be good at arguing about that... Anyway, unlike DONTNEED/FREE we do not have any other OS to implement these features, right? So we shouldn't be tight to existing names. On the other hand I kinda like the reference to the existing names but DEACTIVATE/PAGEOUT seem a good fit to me as well. Unless there is way much better name suggested I would go with one of those. Up to you. -- Michal Hocko SUSE Labs
