On 06/12/2023 10:22, David Hildenbrand wrote: > On 06.12.23 11:13, Ryan Roberts wrote: >> On 05/12/2023 17:21, David Hildenbrand wrote: >>> On 04.12.23 11:20, Ryan Roberts wrote: >>>> Hi All, >>>> >>>> A new week, a new version, a new name... This is v8 of a series to implement >>>> multi-size THP (mTHP) for anonymous memory (previously called "small-sized THP" >>>> and "large anonymous folios"). Matthew objected to "small huge" so hopefully >>>> this fares better. >>>> >>>> The objective of this is to improve performance by allocating larger chunks of >>>> memory during anonymous page faults: >>>> >>>> 1) Since SW (the kernel) is dealing with larger chunks of memory than base >>>> pages, there are efficiency savings to be had; fewer page faults, >>>> batched PTE >>>> and RMAP manipulation, reduced lru list, etc. In short, we reduce kernel >>>> overhead. This should benefit all architectures. >>>> 2) Since we are now mapping physically contiguous chunks of memory, we can take >>>> advantage of HW TLB compression techniques. A reduction in TLB pressure >>>> speeds up kernel and user space. arm64 systems have 2 mechanisms to >>>> coalesce >>>> TLB entries; "the contiguous bit" (architectural) and HPA (uarch). >>>> >>>> This version changes the name and tidies up some of the kernel code and test >>>> code, based on feedback against v7 (see change log for details). >>>> >>>> By default, the existing behaviour (and performance) is maintained. The user >>>> must explicitly enable multi-size THP to see the performance benefit. This is >>>> done via a new sysfs interface (as recommended by David Hildenbrand - thanks to >>>> David for the suggestion)! This interface is inspired by the existing >>>> per-hugepage-size sysfs interface used by hugetlb, provides full backwards >>>> compatibility with the existing PMD-size THP interface, and provides a base for >>>> future extensibility. See [8] for detailed discussion of the interface. >>>> >>>> This series is based on mm-unstable (715b67adf4c8). >>> >>> I took a look at the core pieces. Some things might want some smaller tweaks, >>> but nothing that should stop this from having fun in mm-unstable, and replacing >>> the smaller things as we move forward. >>> >> >> Thanks! I'll address your comments and see if I can post another (final??) >> version next week. > > It's always possible to do incremental changes on top that Andrew will squash in > the end. I even recall that he prefers that way once a series has been in > mm-unstable for a bit, so one can better observe the diff and which effects they > have. > I've responded to all your comments. There are a bunch of changes that I agree would be good to make (and some which I disagree with - would be good if you get a chance to respond). I think I can get all the changes done and tested by Friday. So perhaps it's simplest to keep this out of mm-unstable until then, and put the new version in on Friday? Then if there are any more small changes to do, I can do those as diffs? Thanks, Ryan
