Re: [GIT PULL] afs: Fixes

[David Howells <dhowells@redhat.com>]

Linus Torvalds <torvalds@linux-foundation.org> wrote:

> So I see in the commit message why afs needs to do this, but it's
> worth pointing out that it's
> 
>  (a) impossible to avoid the "inconsistent data" case for writable mmap'ed
>  pages

Doesn't clear_page_dirty_for_io() write-protect the PTE for the page to be
written out, in which case ->page_mkwrite() will get called again before the
page is redirtied?

>  (b) can cause some really nasty latency issues

True, but I think the most common case is a file being opened, written start
to finish and then closed.  Actually, the worst-handled thing I've seen is a
shell script appending a bunch of things to a file because ->flush() syncs the
file each time it is closed:-/

What would you recommend instead?  I'm currently trying and keep track of what
needs to be written so that I only write what's changed to the server, rather
than writing only whole pages.

David