On 26/07/2023 06:53, Yu Zhao wrote: > On Thu, Jul 20, 2023 at 5:30 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >> >> Like page_remove_rmap() but batch-removes the rmap for a range of pages >> belonging to a folio. This can provide a small speedup due to less >> manipuation of the various counters. But more crucially, if removing the >> rmap for all pages of a folio in a batch, there is no need to >> (spuriously) add it to the deferred split list, which saves significant >> cost when there is contention for the split queue lock. >> >> All contained pages are accounted using the order-0 folio (or base page) >> scheme. >> >> page_remove_rmap() is refactored so that it forwards to >> folio_remove_rmap_range() for !compound cases, and both functions now >> share a common epilogue function. The intention here is to avoid >> duplication of code. >> >> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >> --- >> include/linux/rmap.h | 2 + >> mm/rmap.c | 125 ++++++++++++++++++++++++++++++++----------- >> 2 files changed, 97 insertions(+), 30 deletions(-) >> >> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >> index b87d01660412..f578975c12c0 100644 >> --- a/include/linux/rmap.h >> +++ b/include/linux/rmap.h >> @@ -200,6 +200,8 @@ void page_add_file_rmap(struct page *, struct vm_area_struct *, >> bool compound); >> void page_remove_rmap(struct page *, struct vm_area_struct *, >> bool compound); >> +void folio_remove_rmap_range(struct folio *folio, struct page *page, >> + int nr, struct vm_area_struct *vma); > > I prefer folio_remove_rmap_range(page, nr, vma). Passing both the > folio and the starting page seems redundant to me. I prefer to pass folio explicitly because it makes it clear that all pages in the range must belong to the same folio. > > Matthew, is there a convention (function names, parameters, etc.) for > operations on a range of pages within a folio? > > And regarding the refactor, what I have in mind is that > folio_remove_rmap_range() is the core API and page_remove_rmap() is > just a wrapper around it, i.e., folio_remove_rmap_range(page, 1, vma). I tried to do it that way, but the existing page_remove_rmap() also takes a 'compound' parameter; it can operate on compound, thp pages and uses the alternative accounting scheme in this case. I could add a compound parameter to folio_remove_rmap_range() but in that case the range parameters don't make sense - when compound is true we are implicitly operating on the whole folio due to the way the accounting is done. So I felt it was clearer for folio_remove_rmap_range() to deal with small page accounting only. page_remove_rmap() forwards to folio_remove_rmap_range() when compound=false and page_remove_rmap() directly deals with the thp accounting when compound=true. > > Let me post a diff later and see if it makes sense to you.
