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

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Message-ID: <87r0ouw39n.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Thu, 27 Jul 2023 09:29:24 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Yu Zhao <yuzhao@...gle.com>, 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>, 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()

Matthew Wilcox <willy@...radead.org> writes:

> 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.

IIUC, even if 'nr = 1 << PMD_ORDER', we may remove one PMD 'compound'
mapping, or 'nr' PTE mapping.  So, we will still need 'compound' (or
some better name) as parameter.

--
Best Regards,
Huang, Ying