Re: [VM PATCH] rotate_reclaimable_page fails frequently

[Andrew Morton <akpm@osdl.org>]

Rik van Riel <riel@surriel.com> wrote:
>
> On Sun, 5 Feb 2006, Shantanu Goel wrote:
> 
>  > It seems rotate_reclaimable_page fails most of the
>  > time due the page not being on the LRU when kswapd
>  > calls writepage().
> 
>  The question is, why is the page not yet back on the
>  LRU by the time the data write completes ?

Could be they're ext3 pages which were written out by kjournald.  Such
pages are marked dirty but have clean buffers.  ext3_writepage() will
discover that the page is actually clean and will mark it thus without
performing any I/O.

In which case this code in shrink_list():

				/*
				 * A synchronous write - probably a ramdisk.  Go
				 * ahead and try to reclaim the page.
				 */
				if (TestSetPageLocked(page))
					goto keep;
				if (PageDirty(page) || PageWriteback(page))
					goto keep_locked;
				mapping = page_mapping(page);
			case PAGE_CLEAN:
				; /* try to free the page below */

should just go and reclaim the page immediately.

Shantanu, I suggest you add some instrumentation there too, see if it's
working.  (That'll be non-trivial.  Just because we hit PAGE_CLEAN: here
doesn't necessarily mean that the page will be reclaimed).