linux-kernel - Re: [PATCH RFC 05/13] mm/rmap: remove do_page_add_anon

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Date:   Thu, 24 Feb 2022 18:41:20 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Yang Shi <shy828301@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Donald Dutile <ddutile@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
        Liang Zhang <zhangliang5@...wei.com>,
        Pedro Gomes <pedrodemargomes@...il.com>,
        Oded Gabbay <oded.gabbay@...il.com>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH RFC 05/13] mm/rmap: remove do_page_add_anon_rmap()

On 24.02.22 18:29, Linus Torvalds wrote:
> On Thu, Feb 24, 2022 at 4:29 AM David Hildenbrand <david@...hat.com> wrote:
>>
>> ... and instead convert page_add_anon_rmap() to accept flags.
> 
> Can you fix the comment above the RMAP_xyz definitions? That one still says
> 
>   /* bitflags for do_page_add_anon_rmap() */
> 
> that tnow no longer exists.

Oh, yes sure.

> 
> Also, while this kind of code isn't unusual, I think it's still confusing:
> 
>> +               page_add_anon_rmap(page, vma, addr, 0);
> 
> because when reading that, at least I go "what does 0 mean? Is it a
> page offset, or what?"

Yes, I agree.

> 
> It might be a good idea to simply add a
> 
>   #define RMAP_PAGE 0x00
> 
> or something like that, just to have the callers all make it obvious
> that we're talking about that RMAP_xyz bits - even if some of them may
> be default.
> 
> (Then using an enum of a special type is something we do if we want to
> add extra clarity or sparse testing, I don't think there are enough
> users for that to make sense)
> 

Actually, I thought about doing it similarly to what I did in
page_alloc.c with fpi_t:

typedef int __bitwise fpi_t;

#define FPI_NONE		((__force fpi_t)0)


I can do something similar here.

-- 
Thanks,

David / dhildenb