[vlc-devel] commit: mmap: Only use MAP_NOCACHE on platforms that support it. ( Derk-Jan Hartman )

[Derk-Jan Hartman]

On 10 okt 2008, at 14:45, Rémi Denis-Courmont wrote:
> On Fri, 10 Oct 2008 14:16:31 +0200 (CEST), git at videolan.org (git  
> version
> control) wrote:
>> vlc | branch: master | Derk-Jan Hartman <hartman at videolan.org> |  
>> Fri Oct
> 10
>> 14:15:37 2008 +0200| [8dcf947d585d89db6e6b879cc4699d7ca60bb5e4] |
>> committer: Derk-Jan Hartman
>>
>> mmap: Only use MAP_NOCACHE on platforms that support it.
>>
>> That would be Darwin and some BSDs apparently
>
> The OS _knows_ that it can throw this pages out as long as the  
> underlying
> file is in synch o the disk. Even if such a page is still mapped in  
> fact.
>
> I wonder why BSD even needs this flag at all...

The difference is in the priority that this gets.

reasonably guaranteed to be in cache unless impossible
vs.
reasonably lossy caching.

And Linus has been thinking about implementing this as well, but it  
seems that madvise became the more important tool in that area....

DJ