linux-kernel - Re: [PATCH v3 2/3] mm: Implement folio_remove_rmap

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Message-ID: <ZMFNgmlT1JpI0z5+@casper.infradead.org>
Date:   Wed, 26 Jul 2023 17:44:50 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.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 v3 2/3] mm: Implement folio_remove_rmap_range()

On Tue, Jul 25, 2023 at 11:53:26PM -0600, Yu Zhao wrote:
> > +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.
> 
> Matthew, is there a convention (function names, parameters, etc.) for
> operations on a range of pages within a folio?

We've been establishing that convention recently, yes.  It seems
pointless to re-derive the folio from the page when the caller already
has the folio.  I also like Ryan's point that it reinforces that all
pages must be from the same 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).
> 
> Let me post a diff later and see if it makes sense to you.

I think that can make sense.  Because we limit to a single page table,
specifying 'nr = 1 << PMD_ORDER' is the same as 'compound = true'.
Just make it folio, page, nr, vma.  I'd actually prefer it as (vma,
folio, page, nr), but that isn't the convention we've had in rmap up
until now.