Linus Torvalds wrote:
>
> On Wed, 25 Oct 2000, Rik van Riel wrote:
> >
> > OTOH, block-dev readahead makes sense for filesystems where
> > the packing locality is close to the access pattern BUT NOT
> > close to anything the page cache would recognise as being
> > close.
>
> I dunno. The main reason I'd like to get the block devices into the page
> cache is that right now there is no way to mmap them - something that can
> potentially be _very_ useful, regardless of readahead.
>
> And quite frankly, the generic file readahead has been pounded upon and
> tested a lot more than the block device read-ahead ever was. I bet it
> performs better if for no other reason.
And then of course the FS is the LOGICAL level of access to the device -
so
if read ahead matters then it's this level where it should happen -
since
this is the place where actual predictability of the next access
(actually
the assumption that the access will happen at least semi-sequentially)
has good
chances to be right. So you are completely right that the page-cache is
the right place where the rahead logic should take place. I have just
filled
the argumentation gap ;-).
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