Re: [PATCH 3/4] mm: Support only one page_type per page

[David Hildenbrand <david@redhat.com>]

On 21.08.24 19:39, Matthew Wilcox (Oracle) wrote:
> By using a few values in the top byte, users of page_type can store up
> to 24 bits of additional data in page_type.  It also reduces the code
> size as (with replacement of READ_ONCE() with data_race()), the kernel
> can check just a single byte.  eg:
> 
> ffffffff811e3a79:       8b 47 30                mov    0x30(%rdi),%eax
> ffffffff811e3a7c:       55                      push   %rbp
> ffffffff811e3a7d:       48 89 e5                mov    %rsp,%rbp
> ffffffff811e3a80:       25 00 00 00 82          and    $0x82000000,%eax
> ffffffff811e3a85:       3d 00 00 00 80          cmp    $0x80000000,%eax
> ffffffff811e3a8a:       74 4d                   je     ffffffff811e3ad9 <folio_mapping+0x69>
> 
> becomes:
> 
> ffffffff811e3a69:       80 7f 33 f5             cmpb   $0xf5,0x33(%rdi)
> ffffffff811e3a6d:       55                      push   %rbp
> ffffffff811e3a6e:       48 89 e5                mov    %rsp,%rbp
> ffffffff811e3a71:       74 4d                   je     ffffffff811e3ac0 <folio_mapping+0x60>
> 
> replacing three instructions with one.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb