Re: [PATCH v2 2/3] mm: Implement folio_remove_rmap_range()

[Yu Zhao <yuzhao@google.com>]

On Wed, Jul 19, 2023 at 7:55 AM Ryan Roberts <ryan.roberts@arm.com> 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.
>
> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>

I have asked for this before but let me be very clear this time: we
need to generalize the existing functions rather than add more
specialized functions. Otherwise it'd get even harder to maintain down
the road.

folio_remove_rmap_range() needs to replace page_remove_rmap(). IOW,
page_remove_rmap() is just a wrapper around folio_remove_rmap_range().