linux-kernel - Re: [PATCH] mm/hmm: remove redundant check non_swap

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Date:   Fri, 12 Jun 2020 12:53:23 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Jason Gunthorpe <jgg@...lanox.com>,
        Matthew Wilcox <willy@...radead.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm/hmm: remove redundant check non_swap_entry()


On 6/12/20 12:42 PM, Jason Gunthorpe wrote:
> On Fri, Jun 12, 2020 at 12:35:24PM -0700, Matthew Wilcox wrote:
>> On Fri, Jun 12, 2020 at 12:26:18PM -0700, Ralph Campbell wrote:
>>> In zap_pte_range(), the check for non_swap_entry() and
>>> is_device_private_entry() is redundant since the latter is a subset of the
>>> former. Remove the redundant check to simplify the code and for clarity.
>>
>> That is highly configuration dependent.
>>
>> #else /* CONFIG_DEVICE_PRIVATE */
>> ...
>> static inline bool is_device_private_entry(swp_entry_t entry)
>> {
>>          return false;
>> }
> 
> The commit message might be a bit confusing, as it is not a subset, I
> would say that device_private_entry alone is sufficient to tell if the
> entry is private or not.
> 
> For the !CONFIG_DEVICE_PRIVATE case having it wired to false is
> right.
> 
> Jason
> 

How about the following message instead?

In zap_pte_range(), the check for non_swap_entry() and
is_device_private_entry() is unnecessary since the latter is sufficient
to determine if the page is a device private page. Remove the test for
non_swap_entry() to simplify the code and for clarity.