On 27/06/2023 08:49, Yu Zhao wrote: > On Mon, Jun 26, 2023 at 9:30 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: >> >> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >>> >>> Hi All, >>> >>> Following on from the previous RFCv2 [1], this series implements variable order, >>> large folios for anonymous memory. The objective of this is to improve >>> performance by allocating larger chunks of memory during anonymous page faults: >>> >>> - 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, fewer items on lists, etc. In short, we reduce kernel >>> overhead. This should benefit all architectures. >>> - 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 patch set deals with the SW side of things only and based on feedback from >>> the RFC, aims to be the most minimal initial change, upon which future >>> incremental changes can be added. For this reason, the new behaviour is hidden >>> behind a new Kconfig switch, CONFIG_LARGE_ANON_FOLIO, which is disabled by >>> default. Although the code has been refactored to parameterize the desired order >>> of the allocation, when the feature is disabled (by forcing the order to be >>> always 0) my performance tests measure no regression. So I'm hoping this will be >>> a suitable mechanism to allow incremental submissions to the kernel without >>> affecting the rest of the world. >>> >>> The patches are based on top of v6.4 plus Matthew Wilcox's set_ptes() series >>> [2], which is a hard dependency. I'm not sure of Matthew's exact plans for >>> getting that series into the kernel, but I'm hoping we can start the review >>> process on this patch set independently. I have a branch at [3]. >>> >>> I've posted a separate series concerning the HW part (contpte mapping) for arm64 >>> at [4]. >>> >>> >>> Performance >>> ----------- >>> >>> Below results show 2 benchmarks; kernel compilation and speedometer 2.0 (a >>> javascript benchmark running in Chromium). Both cases are running on Ampere >>> Altra with 1 NUMA node enabled, Ubuntu 22.04 and XFS filesystem. Each benchmark >>> is repeated 15 times over 5 reboots and averaged. >>> >>> All improvements are relative to baseline-4k. 'anonfolio-basic' is this series. >>> 'anonfolio' is the full patch set similar to the RFC with the additional changes >>> to the extra 3 fault paths. The rest of the configs are described at [4]. >>> >>> Kernel Compilation (smaller is better): >>> >>> | kernel | real-time | kern-time | user-time | >>> |:----------------|------------:|------------:|------------:| >>> | baseline-4k | 0.0% | 0.0% | 0.0% | >>> | anonfolio-basic | -5.3% | -42.9% | -0.6% | >>> | anonfolio | -5.4% | -46.0% | -0.3% | >>> | contpte | -6.8% | -45.7% | -2.1% | >>> | exefolio | -8.4% | -46.4% | -3.7% | >>> | baseline-16k | -8.7% | -49.2% | -3.7% | >>> | baseline-64k | -10.5% | -66.0% | -3.5% | >>> >>> Speedometer 2.0 (bigger is better): >>> >>> | kernel | runs_per_min | >>> |:----------------|---------------:| >>> | baseline-4k | 0.0% | >>> | anonfolio-basic | 0.7% | >>> | anonfolio | 1.2% | >>> | contpte | 3.1% | >>> | exefolio | 4.2% | >>> | baseline-16k | 5.3% | >> >> Thanks for pushing this forward! >> >>> Changes since RFCv2 >>> ------------------- >>> >>> - Simplified series to bare minimum (on David Hildenbrand's advice) >> >> My impression is that this series still includes many pieces that can >> be split out and discussed separately with followup series. >> >> (I skipped 04/10 and will look at it tomorrow.) > > I went through the series twice. Here what I think a bare minimum > series (easier to review/debug/land) would look like: > 1. a new arch specific function providing a prefered order within (0, > PMD_ORDER). > 2. an extended anon folio alloc API taking that order (02/10, partially). > 3. an updated folio_add_new_anon_rmap() covering the large() && > !pmd_mappable() case (similar to 04/10). > 4. s/folio_test_pmd_mappable/folio_test_large/ in page_remove_rmap() > (06/10, reviewed-by provided). > 5. finally, use the extended anon folio alloc API with the arch > preferred order in do_anonymous_page() (10/10, partially). > > The rest can be split out into separate series and move forward in > parallel with probably a long list of things we need/want to do. Thanks for the fadt review - I really appreciate it! I've responded to many of your comments. I'd appreciate if we can close those points then I will work up a v2. Thanks, Ryan
