On Sun, May 07, 2000 at 12:26:44PM -0700, Linus Torvalds wrote:
>
>
> On Sun, 7 May 2000, Roman V. Shaposhnick wrote:
> >
> > Thus in my *very* humble opinion there was a problem -- pagecache should be
> > generic while it is not.
>
> I like to think of it as "there is a small subset of the page cache
> functionality that is truly generic, but most ofit is very much geared
> towards giving the internal Linux semantics for IO".
Linus, frankly, its your pagecache ;)
> > Linus, please keep in mind, that I do not want to advocate the particular
> > patch. All I want is simple and rational solution for my problems. Thus if
> > for some reason you do not want to tackle with pagecache generalization than
> > would you accept a temporary solution that changes 'readpage' to something
> > like that:
> > int (*readpage)(struct file *, struct page *);
> > and leaves all other things intact ?
>
> Yes. grepping for "readpage" shows that currently we already always
> either:
> - pass in "NULL", or
> - pass in "filp->f_dentry".
>
> So passing in dentry looks to be a bad idea actually: most filesystems do
> not need that field at all (so we do the extra pointer dereference at call
> time for no good reason), and the filesystems that _do_ want to have the
> dentry would really prefer "file" anyway.
>
> So the one case that passes in NULL would continue to pass in NULL; which
> is fine as it is block-file-oriented anyway.
>
> Hmm.. I thought we did the NULL thing for "writepage" too, but it seems
> that we will actually do the swapout() with a known file every time. I'd
> like to change that some day: we should be able to mark the page dirty in
> "struct page", and then rely on shrink_mmap() to be able to write out a
> page without even knowing who dirtied it.
>
> So we don't actually seem to do that yet, but I think we will want to at
> some point. Not 2.4.x, though.
I hate to convince people ( may be that's why I hate lawyers as well ).
And I think that the whole discussion is worthless -- you've pointed out
that you do not want that particular change and that you prefer to have
'struct file *' instead of 'void *' -- that's ok, I guess that's what we
call "the design".
Ok, it seems that the following patch is harmless enough to be applied
even to pre7-7, isn't it ?
Roman.
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