Re: Subtle MM bug

[Daniel Phillips]

Rik van Riel wrote:
> 
> On Tue, 9 Jan 2001, Daniel Phillips wrote:
> > Linus Torvalds wrote:
> > > (This is why I worked so hard at getting the PageDirty semantics right in
> > > the last two months or so - and why I released 2.4.0 when I did. Getting
> > > PageDirty right was the big step to make all of the VM stuff possible in
> > > the first place. Even if it probably looked a bit foolhardy to change the
> > > semantics of "writepage()" quite radically just before 2.4 was released).
> >
> > On the topic of writepage, it's not symmetric with readpage at
> > the moment - it still takes (struct file *).  Is this in the
> > cleanup pipeline?  It looks like nfs_readpage already ignores
> > the struct file *, but maybe some other net filesystems are
> > still depending on it.
> 
> writepage() and readpage() will never be symmetric...
> 
> readpage()
>         program can't continue until data is there
>         reading in larger clusters eats (wastes?) more memory
>         done when we think a process needs data
> 
> writepage()
>         called after the process has written data and moved on
>         writing larger clusters has no influence on memory use
>         often done to free up memory
> 
> Since readpage() needs to tune readahead behaviour, we will
> always want to give it some information (eg. in the file *)
> so it can do the extra things it needs to do.

Which extra information did you have in mind?

--
Daniel