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?
