On Thu, Mar 01, 2018 at 08:17:50AM +0100, Martin Schwidefsky wrote: > On Wed, 28 Feb 2018 14:31:53 -0800 > Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> > > > > I want to use the _mapcount field to record what a page is in use as. > > This can help with debugging and we can also expose that information to > > userspace through /proc/kpageflags to help diagnose memory usage (not > > included as part of this patch set). > > > > First, we need s390 to stop using _mapcount for its own purposes; > > Martin, I hope you have time to look at this patch. I must confess I > > don't quite understand what the different bits are used for in the upper > > nybble of the _mapcount, but I tried to replicate what you were doing > > faithfully. > > Yeah, that is a nasty bit of code. On s390 we have 2K page tables (pte) > but 4K pages. If we use full pages for the pte tables we waste 2K of > memory for each of the tables. So we allocate 4K and split it into two > 2K pieces. Now we have to keep track of the pieces to be able to free > them again. Have you considered to use slab for page table allocation instead? IIRC some architectures practice this already. -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
