linux-kernel - Re: [PATCH RFC v2 2/2] mm: Rework swap handling of zap_pte

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Message-ID: <8a5e44aa-243f-3a9d-e917-09cd3cf6609a@nvidia.com>
Date:   Tue, 16 Nov 2021 00:51:13 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Matthew Wilcox <willy@...radead.org>, Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alistair Popple <apopple@...dia.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH RFC v2 2/2] mm: Rework swap handling of zap_pte_range

On 11/15/21 05:57, Matthew Wilcox wrote:
> On Mon, Nov 15, 2021 at 09:49:51PM +0800, Peter Xu wrote:
>> Clean the code up by merging the device private/exclusive swap entry handling
>> with the rest, then we merge the pte clear operation too.
>>
>> struct* page is defined in multiple places in the function, move it upward.
> 
> Is that actually a good thing?  There was a time when declaring

Yes. It is a very good thing. Having multiple cases of shadowed variables
(in this case I'm using programming language terminology, or what I
remember it as, anyway) provides lots of opportunities to create
hard-to-spot bugs.

> variables more locally helped compilers with liveness analysis and
> register allocation.  Compilers are probably smarter now.
> 

...as long as the above checks out, and I see from Peter's response that
we're OK.


thanks,
-- 
John Hubbard
NVIDIA