Re: grow_dev_page's __GFP_MOVABLE

[Andy Whitcroft <apw@shadowen.org>]

On Fri, Mar 14, 2008 at 10:52:45AM -0800, Badari Pulavarty wrote:
> On Fri, 2008-03-14 at 08:05 -0800, Badari Pulavarty wrote:
> > On Fri, 2008-03-14 at 11:47 +0000, Mel Gorman wrote:
> > > On (13/03/08 16:50), Badari Pulavarty didst pronounce:
> > > > > > <SNIP>
> > > > > > page_owner shows:
> > > > > > 
> > > > > > Page allocated via order 0, mask 0x120050
> > > > > > PFN 30625 Block 7 type 2          Flags      L
> > > > > 
> > > > > This page is indicated as being on the LRU so it should have been possible
> > > > > to reclaim. Is memory hot-remove making any effort to reclaim this page or
> > > > > is it depending only on page migration?
> > > > 
> > > > offline_pages() finds all the pages on LRU and tries to migrate them by
> > > > calling unmap_and_move(). I don't see any explicit attempt to reclaim.
> > > > It tries to migrate the page (move_to_new_page()), but what I have seen
> > > > in the past is that these pages have buffer heads attached to them. 
> > > > So, migrate_page_move_mapping() fails to release the page. (BTW,
> > > > I narrowed this in Oct 2007 and forgot most of the details). I can
> > > > take a closer look again. Can we reclaim these pages easily ?
> > > > 
> > > 
> > > They should be, or huge page allocations using lumpy reclaim would also
> > > be failing all the time.
> > 
> > Hi Mel,
> > 
> > These pages are on LRU and clean. In order to reclaim these pages
> > (looking at pageout()), all we need to do is try_to_release_page().
> > fallback_migrate_page() does this but fails to free it up. What
> > else I can do here to force reclaim these ?
> 
> In other words, caller has a ref on the buffer_head by calling
> getblk(). So, try_to_release_page() would fail since buffer_busy().
> These buffers could be holding meta-data (super block, bitmaps etc.)
> for a file system. Till fs gets rid of the ref, there is nothing
> much we can do. Isn't it ?

Cirtainly when fragmentation avoidance was young we did see a lot of
this as some of the meta-data was badly marked.  What filesystem is this
running on?

-apw

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