Hello, On Tue, 10 Apr 2012 08:52:05 -0400 Vivek Goyal <vgoyal at redhat.com> wrote: > On Tue, Apr 10, 2012 at 08:58:24AM +0900, HATAYAMA Daisuke wrote: > > From: Vivek Goyal <vgoyal at redhat.com> > > Subject: Re: makedumpfile memory usage grows with system memory size > > Date: Mon, 9 Apr 2012 14:57:28 -0400 > > > > > On Fri, Apr 06, 2012 at 06:29:40PM +0900, HATAYAMA Daisuke wrote: > > > > > > [..] > > >> I agree. On the other hand, there is one more thing to consider. The > > >> value of order is in private member of the page descripter. Now > > >> there's no information for private member in VMCOREINFO. If we choose > > >> this method and delete the current one, it's necessary to prepare > > >> vmlinux file for old kernels. > > > > > > What information do you need to access "private" member of "struct page". > > > offset? Can't we extend VMCOREINFO to export this info too? > > > > > > > Yes, I mean offset of private member in page structure. The member > > contains order of the buddy. Extending VMCOREINFO is easy, but we > > cannot do that for old kernels, for which vmlinux is needed > > separately. > > > > This might be the same as what Kumagai-san says he doesn' want to > > change behaviour on kernel versions. > > We can retain both the mechanisms. For newer kernels which export > page->private offset, we can walk through memmap array and prepare a > chunk of bitmap and discard it. For older kernels we can continue to walk > through free pages list and prepare big bitmap in userspace. > > It is desirable to keep mechanism same across kernel versions, but > change is unavoidable as things evolve in newer kernels. So at max > we can provide backward compatibility with old kernels. I said I want to avoid changing behavior based on kernel versions, but it seems difficult as Vivek said. So, I will accept the changing if it is necessary. Now, I will make two prototypes to consider the method to figure out free pages. - a prototype based on _count - a prototype based on PG_buddy (or _mapcount) If prototypes work fine, then we can select the method. Thanks Atsushi Kumagai
