Hi Andrew, David, On 3/14/2023 11:09 AM, Yin Fengwei wrote: > On 3/14/23 02:49, Andrew Morton wrote: >> On Mon, 13 Mar 2023 20:45:21 +0800 Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote: >> >>> This series is trying to bring the batched rmap removing to >>> try_to_unmap_one(). It's expected that the batched rmap >>> removing bring performance gain than remove rmap per page. >>> >>> This series reconstruct the try_to_unmap_one() from: >>> loop: >>> clear and update PTE >>> unmap one page >>> goto loop >>> to: >>> loop: >>> clear and update PTE >>> goto loop >>> unmap the range of folio in one call >>> It is one step to always map/unmap the entire folio in one call. >>> Which can simplify the folio mapcount handling by avoid dealing >>> with each page map/unmap. >>> >>> ... >>> >>> For performance gain demonstration, changed the MADV_PAGEOUT not >>> to split the large folio for page cache and created a micro >>> benchmark mainly as following: >> >> Please remind me why it's necessary to patch the kernel to actually >> performance test this? And why it's proving so hard to demonstrate >> benefits in real-world workloads? >> >> (Yes, this was touched on in earlier discussion, but I do think these >> considerations should be spelled out in the [0/N] changelog). > OK. What about add following in cover letter: > " > The performance gain of this series can be demonstrated with large > folio reclaim. In current kernel, vmscan() path will be benefited by > the changes. But there is no workload/benchmark can show the exact > performance gain for vmscan() path as far as I am aware. > > Another way to demonstrate the performance benefit is using > MADV_PAGEOUT which can trigger page reclaim also. The problem is that > MADV_PAGEOUT always split the large folio because it's not aware of > large folio for page cache currently. To show the performance benefit, > MADV_PAGEOUT is updated not to split the large folio. > > For long term with wider adoption of large folio in kernel (like large > folio for anonymous page), MADV_PAGEOUT needs be updated to handle > large folio as whole to avoid splitting it always. > " I just want to check how I can move this work forward. Is it enough by adding above message? Or still need some other work be done first? Thanks. Regards Yin, Fengwei > > > Regards > Yin, Fengwei > >> >> Thanks. >
