Messages in this thread | | | Subject | Re: [PATCH] take pageout refcount into account for remove_exclusive_swap_page | From | Lee Schermerhorn <> | Date | Tue, 13 May 2008 15:02:50 -0400 |
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On Tue, 2008-05-13 at 14:09 -0400, Rik van Riel wrote: > On Tue, 13 May 2008 13:43:55 -0400 > Lee Schermerhorn <Lee.Schermerhorn@hp.com> wrote: > > > Or, more generally, 2 + N, for an anon page that is mapped [must be > > read-only, right?] by N processes. This can happen after, e.g., fork(). > > Looks like this patch handles the condition just fine, but you might > > want to reflect this in the comment. > > No, this patch only removes a page from the swap cache that is mapped > by one process. The function page_mapped() returns either 1 or 0, not > the same as page_mapcount().
Duh! I was reading "page_mapcount()", 'cause that's what I've been considering using for this purpose.
> > I am not sure if trying to handle swap cache pages that are mapped by > multiple processes could get us into other corner cases and think that > we should probably try to stick to the safe thing for now.
OK. I can test the more general case down the road.
> > Besides, shouldn't anonymous shared pages be COW and relatively rare?
Well, all anon pages are shared right after fork(), right? They only become private once they've been written to. I don't have a feel for the relative numbers of shared anon vs COWed anon--either in general or in the swap cache.
> > > Now, I think I can use this to try to remove anon pages from the swap > > cache when they're mlocked.
I suppose I can just go ahead and use this version with my stress load and count the times when I could have freed the swap cache entry, but didn't because it's mapped in multiple address spaces. Later ... :)
> > > > > + */ > > > +int remove_exclusive_swap_page_ref(struct page *page) > > > +{ > > > + return remove_exclusive_swap_page_count(page, 2 + page_mapped(page)); > > > +} > > > + > > > +/* > > > * Free the swap entry like above, but also try to > > > * free the page cache entry if it is the last user. > > > */ > > > > > > All Rights Reversed > >
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