| Message ID | 20200507103119.11219-6-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtio-mem: paravirtualized memory | expand |
On Thu, May 07, 2020 at 12:31:09PM +0200, David Hildenbrand wrote: > virtio-mem wants to allow to offline memory blocks of which some parts > were unplugged (allocated via alloc_contig_range()), especially, to later > offline and remove completely unplugged memory blocks. The important part > is that PageOffline() has to remain set until the section is offline, so > these pages will never get accessed (e.g., when dumping). The pages should > not be handed back to the buddy (which would require clearing PageOffline() > and result in issues if offlining fails and the pages are suddenly in the > buddy). > > Let's allow to do that by allowing to isolate any PageOffline() page > when offlining. This way, we can reach the memory hotplug notifier > MEM_GOING_OFFLINE, where the driver can signal that he is fine with > offlining this page by dropping its reference count. PageOffline() pages > with a reference count of 0 can then be skipped when offlining the > pages (like if they were free, however they are not in the buddy). > > Anybody who uses PageOffline() pages and does not agree to offline them > (e.g., Hyper-V balloon, XEN balloon, VMWare balloon for 2MB pages) will not > decrement the reference count and make offlining fail when trying to > migrate such an unmovable page. So there should be no observable change. > Same applies to balloon compaction users (movable PageOffline() pages), the > pages will simply be migrated. > > Note 1: If offlining fails, a driver has to increment the reference > count again in MEM_CANCEL_OFFLINE. > > Note 2: A driver that makes use of this has to be aware that re-onlining > the memory block has to be handled by hooking into onlining code > (online_page_callback_t), resetting the page PageOffline() and > not giving them to the buddy. > > Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com> > Acked-by: Michal Hocko <mhocko@suse.com> > Tested-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Juergen Gross <jgross@suse.com> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > Cc: Pavel Tatashin <pavel.tatashin@microsoft.com> > Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com> > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Anthony Yznaga <anthony.yznaga@oracle.com> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Oscar Salvador <osalvador@suse.de> > Cc: Mel Gorman <mgorman@techsingularity.net> > Cc: Mike Rapoport <rppt@linux.ibm.com> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Qian Cai <cai@lca.pw> > Cc: Pingfan Liu <kernelfans@gmail.com> > Signed-off-by: David Hildenbrand <david@redhat.com> Didn't you lose some Andrew Morton's ack on this? > --- > include/linux/page-flags.h | 10 +++++++++ > mm/memory_hotplug.c | 44 +++++++++++++++++++++++++++++--------- > mm/page_alloc.c | 24 +++++++++++++++++++++ > mm/page_isolation.c | 9 ++++++++ > 4 files changed, 77 insertions(+), 10 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 222f6f7b2bb3..6be1aa559b1e 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -777,6 +777,16 @@ PAGE_TYPE_OPS(Buddy, buddy) > * not onlined when onlining the section). > * The content of these pages is effectively stale. Such pages should not > * be touched (read/write/dump/save) except by their owner. > + * > + * If a driver wants to allow to offline unmovable PageOffline() pages without > + * putting them back to the buddy, it can do so via the memory notifier by > + * decrementing the reference count in MEM_GOING_OFFLINE and incrementing the > + * reference count in MEM_CANCEL_OFFLINE. When offlining, the PageOffline() > + * pages (now with a reference count of zero) are treated like free pages, > + * allowing the containing memory block to get offlined. A driver that > + * relies on this feature is aware that re-onlining the memory block will > + * require to re-set the pages PageOffline() and not giving them to the > + * buddy via online_page_callback_t. > */ > PAGE_TYPE_OPS(Offline, offline) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 555137bd0882..936bfe208a6e 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1151,11 +1151,17 @@ struct zone *test_pages_in_a_zone(unsigned long start_pfn, > > /* > * Scan pfn range [start,end) to find movable/migratable pages (LRU pages, > - * non-lru movable pages and hugepages). We scan pfn because it's much > - * easier than scanning over linked list. This function returns the pfn > - * of the first found movable page if it's found, otherwise 0. > + * non-lru movable pages and hugepages). Will skip over most unmovable > + * pages (esp., pages that can be skipped when offlining), but bail out on > + * definitely unmovable pages. > + * > + * Returns: > + * 0 in case a movable page is found and movable_pfn was updated. > + * -ENOENT in case no movable page was found. > + * -EBUSY in case a definitely unmovable page was found. > */ > -static unsigned long scan_movable_pages(unsigned long start, unsigned long end) > +static int scan_movable_pages(unsigned long start, unsigned long end, > + unsigned long *movable_pfn) > { > unsigned long pfn; > > @@ -1167,18 +1173,30 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end) > continue; > page = pfn_to_page(pfn); > if (PageLRU(page)) > - return pfn; > + goto found; > if (__PageMovable(page)) > - return pfn; > + goto found; > + > + /* > + * PageOffline() pages that are not marked __PageMovable() and > + * have a reference count > 0 (after MEM_GOING_OFFLINE) are > + * definitely unmovable. If their reference count would be 0, > + * they could at least be skipped when offlining memory. > + */ > + if (PageOffline(page) && page_count(page)) > + return -EBUSY; > > if (!PageHuge(page)) > continue; > head = compound_head(page); > if (page_huge_active(head)) > - return pfn; > + goto found; > skip = compound_nr(head) - (page - head); > pfn += skip - 1; > } > + return -ENOENT; > +found: > + *movable_pfn = pfn; > return 0; > } > > @@ -1441,7 +1459,8 @@ static int __ref __offline_pages(unsigned long start_pfn, > } > > do { > - for (pfn = start_pfn; pfn;) { > + pfn = start_pfn; > + do { > if (signal_pending(current)) { > ret = -EINTR; > reason = "signal backoff"; > @@ -1451,14 +1470,19 @@ static int __ref __offline_pages(unsigned long start_pfn, > cond_resched(); > lru_add_drain_all(); > > - pfn = scan_movable_pages(pfn, end_pfn); > - if (pfn) { > + ret = scan_movable_pages(pfn, end_pfn, &pfn); > + if (!ret) { > /* > * TODO: fatal migration failures should bail > * out > */ > do_migrate_range(pfn, end_pfn); > } > + } while (!ret); > + > + if (ret != -ENOENT) { > + reason = "unmovable page"; > + goto failed_removal_isolated; > } > > /* > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 64fcaf86763b..6fb3dfca2a97 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -8230,6 +8230,19 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, > if ((flags & MEMORY_OFFLINE) && PageHWPoison(page)) > continue; > > + /* > + * We treat all PageOffline() pages as movable when offlining > + * to give drivers a chance to decrement their reference count > + * in MEM_GOING_OFFLINE in order to indicate that these pages > + * can be offlined as there are no direct references anymore. > + * For actually unmovable PageOffline() where the driver does > + * not support this, we will fail later when trying to actually > + * move these pages that still have a reference count > 0. > + * (false negatives in this function only) > + */ > + if ((flags & MEMORY_OFFLINE) && PageOffline(page)) > + continue; > + > if (__PageMovable(page) || PageLRU(page)) > continue; > > @@ -8650,6 +8663,17 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) > offlined_pages++; > continue; > } > + /* > + * At this point all remaining PageOffline() pages have a > + * reference count of 0 and can simply be skipped. > + */ > + if (PageOffline(page)) { > + BUG_ON(page_count(page)); > + BUG_ON(PageBuddy(page)); > + pfn++; > + offlined_pages++; > + continue; > + } > > BUG_ON(page_count(page)); > BUG_ON(!PageBuddy(page)); > diff --git a/mm/page_isolation.c b/mm/page_isolation.c > index 2c11a38d6e87..f6d07c5f0d34 100644 > --- a/mm/page_isolation.c > +++ b/mm/page_isolation.c > @@ -151,6 +151,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages) > * a bit mask) > * MEMORY_OFFLINE - isolate to offline (!allocate) memory > * e.g., skip over PageHWPoison() pages > + * and PageOffline() pages. > * REPORT_FAILURE - report details about the failure to > * isolate the range > * > @@ -259,6 +260,14 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, > else if ((flags & MEMORY_OFFLINE) && PageHWPoison(page)) > /* A HWPoisoned page cannot be also PageBuddy */ > pfn++; > + else if ((flags & MEMORY_OFFLINE) && PageOffline(page) && > + !page_count(page)) > + /* > + * The responsible driver agreed to skip PageOffline() > + * pages when offlining memory by dropping its > + * reference in MEM_GOING_OFFLINE. > + */ > + pfn++; > else > break; > } > -- > 2.25.3
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 222f6f7b2bb3..6be1aa559b1e 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -777,6 +777,16 @@ PAGE_TYPE_OPS(Buddy, buddy) * not onlined when onlining the section). * The content of these pages is effectively stale. Such pages should not * be touched (read/write/dump/save) except by their owner. + * + * If a driver wants to allow to offline unmovable PageOffline() pages without + * putting them back to the buddy, it can do so via the memory notifier by + * decrementing the reference count in MEM_GOING_OFFLINE and incrementing the + * reference count in MEM_CANCEL_OFFLINE. When offlining, the PageOffline() + * pages (now with a reference count of zero) are treated like free pages, + * allowing the containing memory block to get offlined. A driver that + * relies on this feature is aware that re-onlining the memory block will + * require to re-set the pages PageOffline() and not giving them to the + * buddy via online_page_callback_t. */ PAGE_TYPE_OPS(Offline, offline) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 555137bd0882..936bfe208a6e 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1151,11 +1151,17 @@ struct zone *test_pages_in_a_zone(unsigned long start_pfn, /* * Scan pfn range [start,end) to find movable/migratable pages (LRU pages, - * non-lru movable pages and hugepages). We scan pfn because it's much - * easier than scanning over linked list. This function returns the pfn - * of the first found movable page if it's found, otherwise 0. + * non-lru movable pages and hugepages). Will skip over most unmovable + * pages (esp., pages that can be skipped when offlining), but bail out on + * definitely unmovable pages. + * + * Returns: + * 0 in case a movable page is found and movable_pfn was updated. + * -ENOENT in case no movable page was found. + * -EBUSY in case a definitely unmovable page was found. */ -static unsigned long scan_movable_pages(unsigned long start, unsigned long end) +static int scan_movable_pages(unsigned long start, unsigned long end, + unsigned long *movable_pfn) { unsigned long pfn; @@ -1167,18 +1173,30 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end) continue; page = pfn_to_page(pfn); if (PageLRU(page)) - return pfn; + goto found; if (__PageMovable(page)) - return pfn; + goto found; + + /* + * PageOffline() pages that are not marked __PageMovable() and + * have a reference count > 0 (after MEM_GOING_OFFLINE) are + * definitely unmovable. If their reference count would be 0, + * they could at least be skipped when offlining memory. + */ + if (PageOffline(page) && page_count(page)) + return -EBUSY; if (!PageHuge(page)) continue; head = compound_head(page); if (page_huge_active(head)) - return pfn; + goto found; skip = compound_nr(head) - (page - head); pfn += skip - 1; } + return -ENOENT; +found: + *movable_pfn = pfn; return 0; } @@ -1441,7 +1459,8 @@ static int __ref __offline_pages(unsigned long start_pfn, } do { - for (pfn = start_pfn; pfn;) { + pfn = start_pfn; + do { if (signal_pending(current)) { ret = -EINTR; reason = "signal backoff"; @@ -1451,14 +1470,19 @@ static int __ref __offline_pages(unsigned long start_pfn, cond_resched(); lru_add_drain_all(); - pfn = scan_movable_pages(pfn, end_pfn); - if (pfn) { + ret = scan_movable_pages(pfn, end_pfn, &pfn); + if (!ret) { /* * TODO: fatal migration failures should bail * out */ do_migrate_range(pfn, end_pfn); } + } while (!ret); + + if (ret != -ENOENT) { + reason = "unmovable page"; + goto failed_removal_isolated; } /* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 64fcaf86763b..6fb3dfca2a97 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8230,6 +8230,19 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, if ((flags & MEMORY_OFFLINE) && PageHWPoison(page)) continue; + /* + * We treat all PageOffline() pages as movable when offlining + * to give drivers a chance to decrement their reference count + * in MEM_GOING_OFFLINE in order to indicate that these pages + * can be offlined as there are no direct references anymore. + * For actually unmovable PageOffline() where the driver does + * not support this, we will fail later when trying to actually + * move these pages that still have a reference count > 0. + * (false negatives in this function only) + */ + if ((flags & MEMORY_OFFLINE) && PageOffline(page)) + continue; + if (__PageMovable(page) || PageLRU(page)) continue; @@ -8650,6 +8663,17 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) offlined_pages++; continue; } + /* + * At this point all remaining PageOffline() pages have a + * reference count of 0 and can simply be skipped. + */ + if (PageOffline(page)) { + BUG_ON(page_count(page)); + BUG_ON(PageBuddy(page)); + pfn++; + offlined_pages++; + continue; + } BUG_ON(page_count(page)); BUG_ON(!PageBuddy(page)); diff --git a/mm/page_isolation.c b/mm/page_isolation.c index 2c11a38d6e87..f6d07c5f0d34 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -151,6 +151,7 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages) * a bit mask) * MEMORY_OFFLINE - isolate to offline (!allocate) memory * e.g., skip over PageHWPoison() pages + * and PageOffline() pages. * REPORT_FAILURE - report details about the failure to * isolate the range * @@ -259,6 +260,14 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn, else if ((flags & MEMORY_OFFLINE) && PageHWPoison(page)) /* A HWPoisoned page cannot be also PageBuddy */ pfn++; + else if ((flags & MEMORY_OFFLINE) && PageOffline(page) && + !page_count(page)) + /* + * The responsible driver agreed to skip PageOffline() + * pages when offlining memory by dropping its + * reference in MEM_GOING_OFFLINE. + */ + pfn++; else break; }