Re: [PATCH] cache large files in the page cache

Linus Torvalds (torvalds@transmeta.com)
Wed, 26 May 1999 10:44:02 -0700 (PDT)

On Wed, 26 May 1999, Jakub Jelinek wrote:
>
> I have minor suggestion to the patch. Instead of using vm_index <<
> PAGE_SHIFT and page->key << PAGE_CACHE_SHIFT shifts either choose different
> constant names for this shifting (VM_INDEX_SHIFT and PAGE_KEY_SHIFT) or hide
> these shifts by some pretty macros (you'll need two for each for both
> directions in that case - if you go the macro way, maybe it would be a good
> idea to make vm_index and key type some structure with a single member like
> mm_segment_t for more strict typechecking).

Indeed. An dI would suggest that the shift be limited to at most 9 anyway:
right now I applied the part that disallows non-page-aligned offsets, but
I think that we may in the future allow anonymous mappings again at finer
granularity (somebody made a really good argument about wine for this).

Thinking that the VM mapping shift has to be the same as the page shift is
not necessarily the right thing. With just 9 bits of shift, you still get
large files - 41 bits of files on a 32-bit architecture, and by the time
you want more you _really_ can say that you had better upgrade your CPU.

Linus

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