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

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Date:   Tue, 2 Mar 2021 11:21:35 +1100
From:   Alistair Popple <apopple@...dia.com>
To:     Jason Gunthorpe <jgg@...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 Tuesday, 2 March 2021 4:46:42 AM AEDT Jason Gunthorpe wrote:
> 
> 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?

Correct, and that points to a better name. Maybe is_pfn_swap_entry()? In which 
case adding a helper as Christoph suggested makes some more sense. Eg: 
pfn_swap_entry_to_page()

> > -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?

Yes, sorry I should have called that out. I didn't think loosing the check was 
a big deal, but I can add some checks to some of the call sites which would 
catch a page being incorrectly unlocked.

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

Will add one.

> Transformation looks fine otherwise

Thanks.

 - Alistair
 
> Jason
>