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Subject: Re: [PATCH v14 011/138] mm/lru: Add folio LRU functions
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, Yu Zhao <yuzhao@google.com>,
        Christoph Hellwig <hch@lst.de>,
        David Howells <dhowells@redhat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
References: <20210715033704.692967-1-willy@infradead.org>
 <20210715033704.692967-12-willy@infradead.org>
 <91fb7d5b-9f5f-855e-2c87-dab105d5c977@suse.cz>
 <YRK6y5s8T3qd38G1@casper.infradead.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <3af5a403-2eb9-cc87-f76d-cbbefe5bc82a@suse.cz>
Date:   Wed, 11 Aug 2021 10:58:21 +0200
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On 8/10/21 7:43 PM, Matthew Wilcox wrote:
> On Tue, Aug 10, 2021 at 06:01:16PM +0200, Vlastimil Babka wrote:
>> Actually looking at the git version, which has also this:
>> 
>>  static __always_inline void update_lru_size(struct lruvec *lruvec,
>>                                 enum lru_list lru, enum zone_type zid,
>> -                               int nr_pages)
>> +                               long nr_pages)
>>  {
>> 
>> Why now and here? Some of the functions called from update_lru_size()
>> still take int so this looks arbitrary?
> 
> I'm still a little freaked out about the lack of warning for:
> 
> void f(long n);
> void g(unsigned int n) { f(-n); }
> 
> so I've decided that the count of pages in a folio is always of type
> long.  The actual number is positive, and currently it's between 1 and
> 1024 (inclusive on both bounds), so it's always going to be
> representable in an int.  Narrowing it doesn't cause a bug, so we don't
> need to change nr_pages anywhere, but it does no harm to make functions
> take a long instead of an int (it may even cause slightly better code
> generation, based on the sample of functions I've looked at).
> 
> Maybe changing update_lru_size() in this patch is wrong.  I can drop it
> if you like.

It's fine, knowing it wasn't some rebasing error.