linux-kernel - Re: [PATCH v2 2/3] mm: Implement folio_remove_rmap

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Date:   Wed, 19 Jul 2023 12:23:34 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Ryan Roberts <ryan.roberts@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Yin Fengwei <fengwei.yin@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/3] mm: Implement folio_remove_rmap_range()

On Wed, Jul 19, 2023 at 7:55 AM Ryan Roberts <ryan.roberts@....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@...el.com>
> Reviewed-by: Zi Yan <ziy@...dia.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@....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().