On 11/22/18 at 11:06am, David Hildenbrand wrote: > Right now, pages inflated as part of a balloon driver will be dumped > by dump tools like makedumpfile. While XEN is able to check in the > crash kernel whether a certain pfn is actually backed by memory in the > hypervisor (see xen_oldmem_pfn_is_ram) and optimize this case, dumps of > virtio-balloon, hv-balloon and VMWare balloon inflated memory will > essentially result in zero pages getting allocated by the hypervisor and > the dump getting filled with this data. > > The allocation and reading of zero pages can directly be avoided if a > dumping tool could know which pages only contain stale information not to > be dumped. > > Also for XEN, calling into the kernel and asking the hypervisor if a > pfn is backed can be avoided if the duming tool would skip such pages > right from the beginning. > > Dumping tools have no idea whether a given page is part of a balloon driver > and shall not be dumped. Esp. PG_reserved cannot be used for that purpose > as all memory allocated during early boot is also PG_reserved, see > discussion at [1]. So some other way of indication is required and a new > page flag is frowned upon. > > We have PG_balloon (MAPCOUNT value), which is essentially unused now. I > suggest renaming it to something more generic (PG_offline) to mark pages as > logically offline. This flag can than e.g. also be used by virtio-mem in > the future to mark subsections as offline. Or by other code that wants to > put pages logically offline (e.g. later maybe poisoned pages that shall > no longer be used). > > This series converts PG_balloon to PG_offline, allows dumping tools to > query the value to detect such pages and marks pages in the hv-balloon > and XEN balloon properly as PG_offline. Note that virtio-balloon already > set pages to PG_balloon (and now PG_offline). > > Please note that this is also helpful for a problem we were seeing under > Hyper-V: Dumping logically offline memory (pages kept fake offline while > onlining a section via online_page_callback) would under some condicions > result in a kernel panic when dumping them. > > As I don't have access to neither XEN nor Hyper-V nor VMWare installations, > this was only tested with the virtio-balloon and pages were properly > skipped when dumping. I'll also attach the makedumpfile patch to this > series. > > [1] https://lkml.org/lkml/2018/7/20/566 > > v1 -> v2: > - "kexec: export PG_offline to VMCOREINFO" > -- Add description why it is exported as a macro > - "vmw_balloon: mark inflated pages PG_offline" > -- Use helper function + adapt comments > - "PM / Hibernate: exclude all PageOffline() pages" > -- Perform the check separate from swsusp checks. > - Added RBs/ACKs > > > David Hildenbrand (8): > mm: balloon: update comment about isolation/migration/compaction > mm: convert PG_balloon to PG_offline > kexec: export PG_offline to VMCOREINFO > xen/balloon: mark inflated pages PG_offline > hv_balloon: mark inflated pages PG_offline > vmw_balloon: mark inflated pages PG_offline > PM / Hibernate: use pfn_to_online_page() > PM / Hibernate: exclude all PageOffline() pages > > Documentation/admin-guide/mm/pagemap.rst | 9 ++++--- > drivers/hv/hv_balloon.c | 14 ++++++++-- > drivers/misc/vmw_balloon.c | 32 ++++++++++++++++++++++ > drivers/xen/balloon.c | 3 +++ > fs/proc/page.c | 4 +-- > include/linux/balloon_compaction.h | 34 +++++++++--------------- > include/linux/page-flags.h | 11 +++++--- > include/uapi/linux/kernel-page-flags.h | 2 +- > kernel/crash_core.c | 2 ++ > kernel/power/snapshot.c | 17 +++++++----- > tools/vm/page-types.c | 2 +- > 11 files changed, 90 insertions(+), 40 deletions(-) > > -- > 2.17.2 > This series have been in -next for some days, could we get this in mainline? Andrew, do you have plan about them, maybe next release? Thanks Dave
