Re: [PATCH v14 011/138] mm/lru: Add folio LRU functions

[Vlastimil Babka]

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.