linux-kernel - Re: [PATCH v3 1/8] mm: Remove special swap entry functions

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Message-ID: <20210301174642.GP4247@nvidia.com>
Date:   Mon, 1 Mar 2021 13:46:42 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alistair Popple <apopple@...dia.com>
CC:     <linux-mm@...ck.org>, <nouveau@...ts.freedesktop.org>,
        <bskeggs@...hat.com>, <akpm@...ux-foundation.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <jhubbard@...dia.com>,
        <rcampbell@...dia.com>, <jglisse@...hat.com>, <hch@...radead.org>,
        <daniel@...ll.ch>
Subject: Re: [PATCH v3 1/8] mm: Remove special swap entry functions

On Fri, Feb 26, 2021 at 06:18:25PM +1100, Alistair Popple wrote:
> Remove the migration and device private entry_to_page() and
> entry_to_pfn() inline functions and instead open code them directly.
> This results in shorter code which is easier to understand.
> 
> Signed-off-by: Alistair Popple <apopple@...dia.com>
> ---
>  arch/s390/mm/pgtable.c  |  2 +-
>  fs/proc/task_mmu.c      | 23 +++++++------------
>  include/linux/swap.h    |  4 ++--
>  include/linux/swapops.h | 51 ++++-------------------------------------
>  mm/hmm.c                |  5 ++--
>  mm/memcontrol.c         |  2 +-
>  mm/memory.c             | 10 ++++----
>  mm/migrate.c            |  6 ++---
>  mm/page_vma_mapped.c    |  6 ++---
>  9 files changed, 30 insertions(+), 79 deletions(-)

I wish you could come up with a more descriptive word that special
here

What I understand is this is true when the swap_offset is a pfn?

> -static inline struct page *migration_entry_to_page(swp_entry_t entry)
> -{
> -	struct page *p = pfn_to_page(swp_offset(entry));
> -	/*
> -	 * Any use of migration entries may only occur while the
> -	 * corresponding page is locked
> -	 */
> -	BUG_ON(!PageLocked(compound_head(p)));
> -	return p;

And this constraint has been completely lost?

A comment in front of the is_special_entry explaining all the rule
would help alot

Transformation looks fine otherwise

Jason