On Fri, Jun 20, 2014 at 05:15:43PM +0200, Roger Pau Monn? wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > On 20/06/14 15:28, Konstantin Belousov wrote: > > On Fri, Jun 20, 2014 at 11:35:53AM +0200, Roger Pau Monn? wrote: > >> Hello, > >> > >> I've been looking into the Xen balloon driver, because I've > >> experienced problems when ballooning memory down which AFAICT are > >> also present in the VirtIO balloon driver. The problem I've > >> experienced is that when ballooning memory down, we basically > >> allocate a bunch of memory as WIRED, to make sure nobody tries to > >> swap it do disk, since it will crash the kernel because the > >> memory is not populated. Due to this massive amount of memory > >> allocated as WIRED, user-space programs that try to use mlock > >> will fail because we hit the limit in vm.max_wired. > >> > >> I'm not sure what's the best way to deal with this limitation, > >> should vm.max_wired be changed from the balloon drivers when > >> ballooning down/up? Is there anyway to remove the pages ballooned > >> down from the memory accounting of wired pages? > > > > You could change the type of pages the ballon driver is > > allocating. Instead of wired pages, you may request unmanaged, by > > passing NULL object to vm_page_alloc(). This would also save on > > the trie nodes for managing the radix trie for the object. There > > are still plinks or listq to keep track of the allocated pages. > > Thanks for the info, I have the following patch which fixes the usage > of WIRED for both the Xen and the VirtIO balloon drivers, could > someone please test the VirtIO side? I briefly looked at the xen balloon. You do not need balloon_append(). Use struct vm_page plinks field to link the pages.
pgpeCYPXBGamx.pgp
Description: PGP signature
