Re: [RFC] changes to buffer.c (was Test12 ll_rw_block error)

Marcelo Tosatti
2000-12-22T22:16:53Z

On Fri, 22 Dec 2000, Chris Mason wrote:

>
>
> On Thursday, December 21, 2000 22:38:04 -0200 Marcelo Tosatti
> <marcelo@conectiva.com.br> wrote:
>
> >> Marcelo Tosatti writes:
> >> > It seems your code has a problem with bh flush time.
> >> >
> >> > In flush_dirty_buffers(), a buffer may (if being called from kupdate)
> >> > only be written in case its old enough. (bh->b_flushtime)
> >> >
> >> > If the flush happens for an anonymous buffer, you'll end up writing all
> >> > buffers which are sitting on the same page (with
> >> > block_write_anon_page), but these other buffers are not necessarily
> >> > old enough to be flushed.
> >>
>
> A quick benchmark shows there's room for improvement here. I'll play
> around with a version of block_write_anon_page that tries to be more
> selective when flushing things out.

There is one more nasty issue to deal with.

You only want to take into account the buffer flushtime if
"check_flushtime" parameter is passed as true to flush_dirty_buffers
(which is done by kupdate).

Thinking a bit more about the issue, I dont see any reason why we want to
write all buffers of an anonymous page at
sync_buffers/flush_dirty_buffers.

I think we could simply write the buffer with ll_rw_block() if the page
which this buffer is sitting on does not have mapping->a_ops->writepage
operation defined.

Chris?