Everything should be prepared to stop setting pages PG_reserved when initializing the memmap on memory hotplug. Most importantly, we stop marking ZONE_DEVICE pages PG_reserved. a) We made sure that any code that relied on PG_reserved to detect ZONE_DEVICE memory will no longer rely on PG_reserved - either by using pfn_to_online_page() to exclude them right away or by checking against is_zone_device_page(). b) We made sure that memory blocks with holes cannot be offlined and therefore also not onlined. We have quite some code that relies on memory holes being marked PG_reserved. This is now not an issue anymore. generic_online_page() still calls __free_pages_core(), which performs __ClearPageReserved(p). AFAIKS, this should not hurt. It is worth nothing that the users of online_page_callback_t might see a change. E.g., until now, pages not freed to the buddy by the HyperV balloonm were set PG_reserved until freed via generic_online_page(). Now, they would look like ordinarily allocated pages (refcount == 1). This callback is used by the XEN balloon and the HyperV balloon. To not introduce any silent errors, keep marking the pages PG_reserved. We can most probably stop doing that, but have to double check if there are issues (e.g., offlining code aborts right away in has_unmovable_pages() when it runs into a PageReserved(page)) Update the documentation at various places. Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx> Cc: Sasha Levin <sashal@xxxxxxxxxx> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx> Cc: Pavel Tatashin <pavel.tatashin@xxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Anthony Yznaga <anthony.yznaga@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- drivers/hv/hv_balloon.c | 6 ++++++ drivers/xen/balloon.c | 7 +++++++ include/linux/page-flags.h | 8 +------- mm/memory_hotplug.c | 17 +++++++---------- mm/page_alloc.c | 11 ----------- 5 files changed, 21 insertions(+), 28 deletions(-) diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index c722079d3c24..3214b0ef5247 100644 --- a/drivers/hv/hv_balloon.c +++ b/drivers/hv/hv_balloon.c @@ -670,6 +670,12 @@ static struct notifier_block hv_memory_nb = { /* Check if the particular page is backed and can be onlined and online it. */ static void hv_page_online_one(struct hv_hotadd_state *has, struct page *pg) { + /* + * TODO: The core used to mark the pages reserved. Most probably + * we can stop doing that now. + */ + __SetPageReserved(pg); + if (!has_pfn_is_backed(has, page_to_pfn(pg))) { if (!PageOffline(pg)) __SetPageOffline(pg); diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 4f2e78a5e4db..af69f057913a 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -374,6 +374,13 @@ static void xen_online_page(struct page *page, unsigned int order) mutex_lock(&balloon_mutex); for (i = 0; i < size; i++) { p = pfn_to_page(start_pfn + i); + /* + * TODO: The core used to mark the pages reserved. Most probably + * we can stop doing that now. However, especially + * alloc_xenballooned_pages() left PG_reserved set + * on pages that can get mapped to user space. + */ + __SetPageReserved(p); balloon_append(p); } mutex_unlock(&balloon_mutex); diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index f91cb8898ff0..d4f85d866b71 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -30,24 +30,18 @@ * - Pages falling into physical memory gaps - not IORESOURCE_SYSRAM. Trying * to read/write these pages might end badly. Don't touch! * - The zero page(s) - * - Pages not added to the page allocator when onlining a section because - * they were excluded via the online_page_callback() or because they are - * PG_hwpoison. * - Pages allocated in the context of kexec/kdump (loaded kernel image, * control pages, vmcoreinfo) * - MMIO/DMA pages. Some architectures don't allow to ioremap pages that are * not marked PG_reserved (as they might be in use by somebody else who does * not respect the caching strategy). - * - Pages part of an offline section (struct pages of offline sections should - * not be trusted as they will be initialized when first onlined). * - MCA pages on ia64 * - Pages holding CPU notes for POWER Firmware Assisted Dump - * - Device memory (e.g. PMEM, DAX, HMM) * Some PG_reserved pages will be excluded from the hibernation image. * PG_reserved does in general not hinder anybody from dumping or swapping * and is no longer required for remap_pfn_range(). ioremap might require it. * Consequently, PG_reserved for a page mapped into user space can indicate - * the zero page, the vDSO, MMIO pages or device memory. + * the zero page, the vDSO, or MMIO pages. * * The PG_private bitflag is set on pagecache pages if they contain filesystem * specific data (which is normally at page->private). It can be used by diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 7210f4375279..9fbcdeaf0339 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -501,9 +501,7 @@ static void __remove_section(unsigned long pfn, unsigned long nr_pages, * @altmap: alternative device page map or %NULL if default memmap is used * * Generic helper function to remove section mappings and sysfs entries - * for the section of the memory we are removing. Caller needs to make - * sure that pages are marked reserved and zones are adjust properly by - * calling offline_pages(). + * for the section of the memory we are removing. */ void __remove_pages(unsigned long pfn, unsigned long nr_pages, struct vmem_altmap *altmap) @@ -584,9 +582,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages, int order; /* - * Online the pages. The callback might decide to keep some pages - * PG_reserved (to add them to the buddy later), but we still account - * them as being online/belonging to this zone ("present"). + * Online the pages. The callback might decide to not free some pages + * (to add them to the buddy later), but we still account them as + * being online/belonging to this zone ("present"). */ for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) { order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn))); @@ -659,8 +657,7 @@ static void __meminit resize_pgdat_range(struct pglist_data *pgdat, unsigned lon } /* * Associate the pfn range with the given zone, initializing the memmaps - * and resizing the pgdat/zone data to span the added pages. After this - * call, all affected pages are PG_reserved. + * and resizing the pgdat/zone data to span the added pages. */ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, unsigned long nr_pages, struct vmem_altmap *altmap) @@ -684,8 +681,8 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, /* * TODO now we have a visible range of pages which are not associated * with their zone properly. Not nice but set_pfnblock_flags_mask - * expects the zone spans the pfn range. All the pages in the range - * are reserved so nobody should be touching them so we should be safe + * expects the zone spans the pfn range. The sections are not yet + * marked online so nobody should be touching the memmap. */ memmap_init_zone(nr_pages, nid, zone_idx(zone), start_pfn, MEMMAP_HOTPLUG, altmap); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e153280bde9a..29787ac4aeb8 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5927,8 +5927,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone, page = pfn_to_page(pfn); __init_single_page(page, pfn, zone, nid); - if (context == MEMMAP_HOTPLUG) - __SetPageReserved(page); /* * Mark the block movable so that blocks are reserved for @@ -5980,15 +5978,6 @@ void __ref memmap_init_zone_device(struct zone *zone, __init_single_page(page, pfn, zone_idx, nid); - /* - * Mark page reserved as it will need to wait for onlining - * phase for it to be fully associated with a zone. - * - * We can use the non-atomic __set_bit operation for setting - * the flag as we are still initializing the pages. - */ - __SetPageReserved(page); - /* * ZONE_DEVICE pages union ->lru with a ->pgmap back pointer * and zone_device_data. It is a bug if a ZONE_DEVICE page is -- 2.21.0 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel