Re: [PATCH] read-modify-write page updating

[Peter Staubach <staubach@redhat.com>]

Trond Myklebust wrote:
>
> It might also be nice to put the above test in a little inlined helper
> function (called nfs_want_read_modify_write() ?).
>
>   

Good suggestion.

> So, a number of questions spring to mind:
>
>      1. What if we're extending the file? We might not need to read the
>         page at all in that case (see nfs_write_end()).
>   

Yup.

>      2. What if the page is already dirty or is carrying an uncommitted
>         unstable write?
>   

Yup.

>      3. We might want to try to avoid looping more than once here. If
>         the kernel is very low on memory, we might just want to write
>         out the data rather than read the page and risk having the VM
>         eject it before we can dirty it.
>   

Yup.

>      4. Should we be starting an async readahead on the next page?
>         Single page sized reads can be a nuisance too, if you are
>         writing huge amounts of data.

This one is tough.  It sounds good, but seems difficult to implement.

I think that this could be viewed as an optimization.

       ps