Hello,
> When pageout a dirty page, try to piggy back more consecutive dirty
> pages (up to 512KB) to improve IO efficiency.
>
> Only ext3/reiserfs which don't have its own aops->writepages are
> supported in this initial version.
>
[...]
> /*
> + * only write_cache_pages() supports for_reclaim for now
> + */
> + if (!mapping->a_ops->writepages) {
> + wbc.range_start = (page->index + 1) << PAGE_CACHE_SHIFT;
> + wbc.nr_to_write = LUMPY_PAGEOUT_PAGES - 1;
> + generic_writepages(mapping, &wbc);
> + }
This might end up calling ->writepage() on a page_mapped() page,
which used to be a problem, at least for shmem (see
BUG_ON(page_mapped(page)) in shmem_writepage()).
I tried to do a similar thing in the past, but eventually decided
do explicitly call ->writepage() in a loop from vmscan.c. This
way one can also filter out referenced and active pages. See
http://linuxhacker.ru/~nikita/patches/2.6.14-rc5/05-cluster-pageout.patch,
it also contains a comment explaining shmem problem.
Thank you,
Nikita.
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