Re: journaling & VM (was: Re: reiserfs being part of the kernel: it'snot just the code)

Stephen C. Tweedie
2000-06-07T21:24:21Z

Hi,

On Wed, Jun 07, 2000 at 10:56:17PM +0200, Juan J. Quintela wrote:
>
> >> I'd like to be able to keep stuff simple in the shrink_mmap
> >> "equivalent" I'm working on. Something like:
> >>
> >> if (PageDirty(page) && page->mapping && page->mapping->flush)
> >> maxlaunder -= page->mapping->flush();
>
> sct> That looks ideal.
>
> But this is supposed to flush that _page_, at least in the normal
> case.

All transactional filesystems will have ordering constraints which
the core VM cannot know about. In that case, the filesystem may
simply have no choice about cleaning and unpinning pages in a given
order. For actually removing a page from memory, evicting precisely
the right page is far more important, but for writeback, it's
controlling the amount of dirty/pinned data from the various different
sources which counts.

Cheers,
Stephen