[PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

[PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

[David Hildenbrand]

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>

With an altmap, the memmap falling into the reserved altmap space are
not initialized and, therefore, contain a garbage NID and a garbage
zone. Make sure to read the NID/zone from a memmap that was initialzed.

This fixes a kernel crash that is observed when destroying a namespace:

[   81.356173] kernel BUG at include/linux/mm.h:1107!
cpu 0x1: Vector: 700 (Program Check) at [c000000274087890]
    pc: c0000000004b9728: memunmap_pages+0x238/0x340
    lr: c0000000004b9724: memunmap_pages+0x234/0x340
...
    pid   = 3669, comm = ndctl
kernel BUG at include/linux/mm.h:1107!
[c000000274087ba0] c0000000009e3500 devm_action_release+0x30/0x50
[c000000274087bc0] c0000000009e4758 release_nodes+0x268/0x2d0
[c000000274087c30] c0000000009dd144 device_release_driver_internal+0x174/0x240
[c000000274087c70] c0000000009d9dfc unbind_store+0x13c/0x190
[c000000274087cb0] c0000000009d8a24 drv_attr_store+0x44/0x60
[c000000274087cd0] c0000000005a7470 sysfs_kf_write+0x70/0xa0
[c000000274087d10] c0000000005a5cac kernfs_fop_write+0x1ac/0x290
[c000000274087d60] c0000000004be45c __vfs_write+0x3c/0x70
[c000000274087d80] c0000000004c26e4 vfs_write+0xe4/0x200
[c000000274087dd0] c0000000004c2a6c ksys_write+0x7c/0x140
[c000000274087e20] c00000000000bbd0 system_call+0x5c/0x68

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
[ minimze code changes, rephrase description ]
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memremap.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/memremap.c b/mm/memremap.c
index 557e53c6fb46..8c2fb44c3b4d 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -123,6 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
 void memunmap_pages(struct dev_pagemap *pgmap)
 {
 	struct resource *res = &pgmap->res;
+	struct page *first_page;
 	unsigned long pfn;
 	int nid;
 
@@ -131,14 +132,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 		put_page(pfn_to_page(pfn));
 	dev_pagemap_cleanup(pgmap);
 
+	/* make sure to access a memmap that was actually initialized */
+	first_page = pfn_to_page(pfn_first(pgmap));
+
 	/* pages are dead and unused, undo the arch mapping */
-	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
+	nid = page_to_nid(first_page);
 
 	mem_hotplug_begin();
 	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
-		pfn = PHYS_PFN(res->start);
-		__remove_pages(page_zone(pfn_to_page(pfn)), pfn,
-				 PHYS_PFN(resource_size(res)), NULL);
+		__remove_pages(page_zone(first_page), PHYS_PFN(res->start),
+			       PHYS_PFN(resource_size(res)), NULL);
 	} else {
 		arch_remove_memory(nid, res->start, resource_size(res),
 				pgmap_altmap(pgmap));
-- 
2.21.0


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[PATCH v6 02/10] mm/memmap_init: Update variable name in memmap_init_zone

[David Hildenbrand]

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>

The third argument is actually number of pages. Changes the variable name
from size to nr_pages to indicate this better.

No functional change in this patch.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
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: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Pavel Tatashin <pavel.tatashin@microsoft.com>
Cc: Alexander Potapenko <glider@google.com>
Reviewed-by: Pankaj Gupta <pagupta@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/page_alloc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 15c2050c629b..b0b2d5464000 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5936,10 +5936,10 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 #ifdef CONFIG_ZONE_DEVICE
 void __ref memmap_init_zone_device(struct zone *zone,
 				   unsigned long start_pfn,
-				   unsigned long size,
+				   unsigned long nr_pages,
 				   struct dev_pagemap *pgmap)
 {
-	unsigned long pfn, end_pfn = start_pfn + size;
+	unsigned long pfn, end_pfn = start_pfn + nr_pages;
 	struct pglist_data *pgdat = zone->zone_pgdat;
 	struct vmem_altmap *altmap = pgmap_altmap(pgmap);
 	unsigned long zone_idx = zone_idx(zone);
@@ -5956,7 +5956,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 	 */
 	if (altmap) {
 		start_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
-		size = end_pfn - start_pfn;
+		nr_pages = end_pfn - start_pfn;
 	}
 
 	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
@@ -6003,7 +6003,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 	}
 
 	pr_info("%s initialised %lu pages in %ums\n", __func__,
-		size, jiffies_to_msecs(jiffies - start));
+		nr_pages, jiffies_to_msecs(jiffies - start));
 }
 
 #endif
-- 
2.21.0


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[PATCH v6 03/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_pgdat_span()

[David Hildenbrand]

We might use the nid of memmaps that were never initialized. For
example, if the memmap was poisoned, we will crash the kernel in
pfn_to_nid() right now. Let's use the calculated boundaries of the separate
zones instead. This now also avoids having to iterate over a whole bunch of
subsections again, after shrinking one zone.

Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory
hotplug"), the memmap was initialized to 0 and the node was set to the
right value. After that commit, the node might be garbage.

We'll have to fix shrink_zone_span() next.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 72 ++++++++++-----------------------------------
 1 file changed, 15 insertions(+), 57 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 680b4b3e57d9..86b4dc18e831 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -436,67 +436,25 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 	zone_span_writeunlock(zone);
 }
 
-static void shrink_pgdat_span(struct pglist_data *pgdat,
-			      unsigned long start_pfn, unsigned long end_pfn)
+static void update_pgdat_span(struct pglist_data *pgdat)
 {
-	unsigned long pgdat_start_pfn = pgdat->node_start_pfn;
-	unsigned long p = pgdat_end_pfn(pgdat); /* pgdat_end_pfn namespace clash */
-	unsigned long pgdat_end_pfn = p;
-	unsigned long pfn;
-	int nid = pgdat->node_id;
-
-	if (pgdat_start_pfn == start_pfn) {
-		/*
-		 * If the section is smallest section in the pgdat, it need
-		 * shrink pgdat->node_start_pfn and pgdat->node_spanned_pages.
-		 * In this case, we find second smallest valid mem_section
-		 * for shrinking zone.
-		 */
-		pfn = find_smallest_section_pfn(nid, NULL, end_pfn,
-						pgdat_end_pfn);
-		if (pfn) {
-			pgdat->node_start_pfn = pfn;
-			pgdat->node_spanned_pages = pgdat_end_pfn - pfn;
-		}
-	} else if (pgdat_end_pfn == end_pfn) {
-		/*
-		 * If the section is biggest section in the pgdat, it need
-		 * shrink pgdat->node_spanned_pages.
-		 * In this case, we find second biggest valid mem_section for
-		 * shrinking zone.
-		 */
-		pfn = find_biggest_section_pfn(nid, NULL, pgdat_start_pfn,
-					       start_pfn);
-		if (pfn)
-			pgdat->node_spanned_pages = pfn - pgdat_start_pfn + 1;
-	}
-
-	/*
-	 * If the section is not biggest or smallest mem_section in the pgdat,
-	 * it only creates a hole in the pgdat. So in this case, we need not
-	 * change the pgdat.
-	 * But perhaps, the pgdat has only hole data. Thus it check the pgdat
-	 * has only hole or not.
-	 */
-	pfn = pgdat_start_pfn;
-	for (; pfn < pgdat_end_pfn; pfn += PAGES_PER_SUBSECTION) {
-		if (unlikely(!pfn_valid(pfn)))
-			continue;
-
-		if (pfn_to_nid(pfn) != nid)
-			continue;
+	unsigned long node_start_pfn = 0, node_end_pfn = 0;
+	struct zone *zone;
 
-		/* Skip range to be removed */
-		if (pfn >= start_pfn && pfn < end_pfn)
-			continue;
+	for (zone = pgdat->node_zones;
+	     zone < pgdat->node_zones + MAX_NR_ZONES; zone++) {
+		unsigned long zone_end_pfn = zone->zone_start_pfn +
+					     zone->spanned_pages;
 
-		/* If we find valid section, we have nothing to do */
-		return;
+		/* No need to lock the zones, they can't change. */
+		if (zone_end_pfn > node_end_pfn)
+			node_end_pfn = zone_end_pfn;
+		if (zone->zone_start_pfn < node_start_pfn)
+			node_start_pfn = zone->zone_start_pfn;
 	}
 
-	/* The pgdat has no valid section */
-	pgdat->node_start_pfn = 0;
-	pgdat->node_spanned_pages = 0;
+	pgdat->node_start_pfn = node_start_pfn;
+	pgdat->node_spanned_pages = node_end_pfn - node_start_pfn;
 }
 
 static void __remove_zone(struct zone *zone, unsigned long start_pfn,
@@ -507,7 +465,7 @@ static void __remove_zone(struct zone *zone, unsigned long start_pfn,
 
 	pgdat_resize_lock(zone->zone_pgdat, &flags);
 	shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
-	shrink_pgdat_span(pgdat, start_pfn, start_pfn + nr_pages);
+	update_pgdat_span(pgdat);
 	pgdat_resize_unlock(zone->zone_pgdat, &flags);
 }
 
-- 
2.21.0


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[PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span()

[David Hildenbrand]

Let's limit shrinking to !ZONE_DEVICE so we can fix the current code. We
should never try to touch the memmap of offline sections where we could
have uninitialized memmaps and could trigger BUGs when calling
page_to_nid() on poisoned pages.

There is no reliable way to distinguish an uninitialized memmap from an
initialized memmap that belongs to ZONE_DEVICE, as we don't have
anything like SECTION_IS_ONLINE we can use similar to
pfn_to_online_section() for !ZONE_DEVICE memory. E.g.,
set_zone_contiguous() similarly relies on pfn_to_online_section() and
will therefore never set a ZONE_DEVICE zone consecutive. Stopping to
shrink the ZONE_DEVICE therefore results in no observable changes,
besides /proc/zoneinfo indicating different boundaries - something we
can totally live with.

Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory
hotplug"), the memmap was initialized with 0 and the node with the
right value. So the zone might be wrong but not garbage. After that
commit, both the zone and the node will be garbage when touching
uninitialized memmaps.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 86b4dc18e831..f96608d24f6a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -331,7 +331,7 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
 				     unsigned long end_pfn)
 {
 	for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) {
-		if (unlikely(!pfn_valid(start_pfn)))
+		if (unlikely(!pfn_to_online_page(start_pfn)))
 			continue;
 
 		if (unlikely(pfn_to_nid(start_pfn) != nid))
@@ -356,7 +356,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
 	/* pfn is the end pfn of a memory section. */
 	pfn = end_pfn - 1;
 	for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) {
-		if (unlikely(!pfn_valid(pfn)))
+		if (unlikely(!pfn_to_online_page(pfn)))
 			continue;
 
 		if (unlikely(pfn_to_nid(pfn) != nid))
@@ -415,7 +415,7 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 	 */
 	pfn = zone_start_pfn;
 	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
-		if (unlikely(!pfn_valid(pfn)))
+		if (unlikely(!pfn_to_online_page(pfn)))
 			continue;
 
 		if (page_zone(pfn_to_page(pfn)) != zone)
@@ -463,6 +463,16 @@ static void __remove_zone(struct zone *zone, unsigned long start_pfn,
 	struct pglist_data *pgdat = zone->zone_pgdat;
 	unsigned long flags;
 
+#ifdef CONFIG_ZONE_DEVICE
+	/*
+	 * Zone shrinking code cannot properly deal with ZONE_DEVICE. So
+	 * we will not try to shrink the zones - which is okay as
+	 * set_zone_contiguous() cannot deal with ZONE_DEVICE either way.
+	 */
+	if (zone_idx(zone) == ZONE_DEVICE)
+		return;
+#endif
+
 	pgdat_resize_lock(zone->zone_pgdat, &flags);
 	shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
 	update_pgdat_span(pgdat);
-- 
2.21.0


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[PATCH v6 06/10] mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone()

[David Hildenbrand]

Let's poison the pages similar to when adding new memory in
sparse_add_section(). Also call remove_pfn_range_from_zone() from
memunmap_pages(), so we can poison the memmap from there as well.

While at it, calculate the pfn in memunmap_pages() only once.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 3 +++
 mm/memremap.c       | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 5b003ffa5dc9..bf5173e7913d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -464,6 +464,9 @@ void __ref remove_pfn_range_from_zone(struct zone *zone,
 	struct pglist_data *pgdat = zone->zone_pgdat;
 	unsigned long flags;
 
+	/* Poison struct pages because they are now uninitialized again. */
+	page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages);
+
 #ifdef CONFIG_ZONE_DEVICE
 	/*
 	 * Zone shrinking code cannot properly deal with ZONE_DEVICE. So
diff --git a/mm/memremap.c b/mm/memremap.c
index 70263e6f093e..7fed8bd32a18 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -139,6 +139,8 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 	nid = page_to_nid(first_page);
 
 	mem_hotplug_begin();
+	remove_pfn_range_from_zone(page_zone(first_page), PHYS_PFN(res->start),
+				   PHYS_PFN(resource_size(res)));
 	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
 		__remove_pages(PHYS_PFN(res->start),
 			       PHYS_PFN(resource_size(res)), NULL);
-- 
2.21.0


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[PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn

[David Hildenbrand]

With shrink_pgdat_span() out of the way, we now always have a valid
zone.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index bf5173e7913d..f294918f7211 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -337,7 +337,7 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
 		if (unlikely(pfn_to_nid(start_pfn) != nid))
 			continue;
 
-		if (zone && zone != page_zone(pfn_to_page(start_pfn)))
+		if (zone != page_zone(pfn_to_page(start_pfn)))
 			continue;
 
 		return start_pfn;
@@ -362,7 +362,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
 		if (unlikely(pfn_to_nid(pfn) != nid))
 			continue;
 
-		if (zone && zone != page_zone(pfn_to_page(pfn)))
+		if (zone != page_zone(pfn_to_page(pfn)))
 			continue;
 
 		return pfn;
-- 
2.21.0


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[PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

If we have holes, the holes will automatically get detected and removed
once we remove the next bigger/smaller section. The extra checks can
go.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 34 +++++++---------------------------
 1 file changed, 7 insertions(+), 27 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index f294918f7211..8dafa1ba8d9f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 		if (pfn) {
 			zone->zone_start_pfn = pfn;
 			zone->spanned_pages = zone_end_pfn - pfn;
+		} else {
+			zone->zone_start_pfn = 0;
+			zone->spanned_pages = 0;
 		}
 	} else if (zone_end_pfn == end_pfn) {
 		/*
@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 					       start_pfn);
 		if (pfn)
 			zone->spanned_pages = pfn - zone_start_pfn + 1;
+		else {
+			zone->zone_start_pfn = 0;
+			zone->spanned_pages = 0;
+		}
 	}
-
-	/*
-	 * The section is not biggest or smallest mem_section in the zone, it
-	 * only creates a hole in the zone. So in this case, we need not
-	 * change the zone. But perhaps, the zone has only hole data. Thus
-	 * it check the zone has only hole or not.
-	 */
-	pfn = zone_start_pfn;
-	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
-		if (unlikely(!pfn_to_online_page(pfn)))
-			continue;
-
-		if (page_zone(pfn_to_page(pfn)) != zone)
-			continue;
-
-		/* Skip range to be removed */
-		if (pfn >= start_pfn && pfn < end_pfn)
-			continue;
-
-		/* If we find valid section, we have nothing to do */
-		zone_span_writeunlock(zone);
-		return;
-	}
-
-	/* The zone has no valid section */
-	zone->zone_start_pfn = 0;
-	zone->spanned_pages = 0;
 	zone_span_writeunlock(zone);
 }
 
-- 
2.21.0


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[PATCH v6 09/10] mm/memory_hotplug: Drop local variables in shrink_zone_span()

[David Hildenbrand]

Get rid of the unnecessary local variables.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8dafa1ba8d9f..843481bd507d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -374,14 +374,11 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
 static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 			     unsigned long end_pfn)
 {
-	unsigned long zone_start_pfn = zone->zone_start_pfn;
-	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
-	unsigned long zone_end_pfn = z;
 	unsigned long pfn;
 	int nid = zone_to_nid(zone);
 
 	zone_span_writelock(zone);
-	if (zone_start_pfn == start_pfn) {
+	if (zone->zone_start_pfn == start_pfn) {
 		/*
 		 * If the section is smallest section in the zone, it need
 		 * shrink zone->zone_start_pfn and zone->zone_spanned_pages.
@@ -389,25 +386,25 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 		 * for shrinking zone.
 		 */
 		pfn = find_smallest_section_pfn(nid, zone, end_pfn,
-						zone_end_pfn);
+						zone_end_pfn(zone));
 		if (pfn) {
+			zone->spanned_pages = zone_end_pfn(zone) - pfn;
 			zone->zone_start_pfn = pfn;
-			zone->spanned_pages = zone_end_pfn - pfn;
 		} else {
 			zone->zone_start_pfn = 0;
 			zone->spanned_pages = 0;
 		}
-	} else if (zone_end_pfn == end_pfn) {
+	} else if (zone_end_pfn(zone) == end_pfn) {
 		/*
 		 * If the section is biggest section in the zone, it need
 		 * shrink zone->spanned_pages.
 		 * In this case, we find second biggest valid mem_section for
 		 * shrinking zone.
 		 */
-		pfn = find_biggest_section_pfn(nid, zone, zone_start_pfn,
+		pfn = find_biggest_section_pfn(nid, zone, zone->zone_start_pfn,
 					       start_pfn);
 		if (pfn)
-			zone->spanned_pages = pfn - zone_start_pfn + 1;
+			zone->spanned_pages = pfn - zone->zone_start_pfn + 1;
 		else {
 			zone->zone_start_pfn = 0;
 			zone->spanned_pages = 0;
-- 
2.21.0


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[PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[David Hildenbrand]

Let's drop the basically unused section stuff and simplify.

Also, let's use a shorter variant to calculate the number of pages to
the next section boundary.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory_hotplug.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 843481bd507d..2275240cfa10 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -490,25 +490,20 @@ static void __remove_section(unsigned long pfn, unsigned long nr_pages,
 void __remove_pages(unsigned long pfn, unsigned long nr_pages,
 		    struct vmem_altmap *altmap)
 {
+	const unsigned long end_pfn = pfn + nr_pages;
+	unsigned long cur_nr_pages;
 	unsigned long map_offset = 0;
-	unsigned long nr, start_sec, end_sec;
 
 	map_offset = vmem_altmap_offset(altmap);
 
 	if (check_pfn_span(pfn, nr_pages, "remove"))
 		return;
 
-	start_sec = pfn_to_section_nr(pfn);
-	end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
-	for (nr = start_sec; nr <= end_sec; nr++) {
-		unsigned long pfns;
-
+	for (; pfn < end_pfn; pfn += cur_nr_pages) {
 		cond_resched();
-		pfns = min(nr_pages, PAGES_PER_SECTION
-				- (pfn & ~PAGE_SECTION_MASK));
-		__remove_section(pfn, pfns, map_offset, altmap);
-		pfn += pfns;
-		nr_pages -= pfns;
+		/* Select all remaining pages up to the next section boundary */
+		cur_nr_pages = min(end_pfn - pfn, -(pfn | PAGE_SECTION_MASK));
+		__remove_section(pfn, cur_nr_pages, map_offset, altmap);
 		map_offset = 0;
 	}
 }
-- 
2.21.0


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Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

[Damian Tometzki]

Hello David,

patch 05/10 is missing in the patch series. 


On Sun, 06. Oct 10:56, David Hildenbrand wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
> 
> With an altmap, the memmap falling into the reserved altmap space are
> not initialized and, therefore, contain a garbage NID and a garbage
> zone. Make sure to read the NID/zone from a memmap that was initialzed.
> 
> This fixes a kernel crash that is observed when destroying a namespace:
> 
> [   81.356173] kernel BUG at include/linux/mm.h:1107!
> cpu 0x1: Vector: 700 (Program Check) at [c000000274087890]
>     pc: c0000000004b9728: memunmap_pages+0x238/0x340
>     lr: c0000000004b9724: memunmap_pages+0x234/0x340
> ...
>     pid   = 3669, comm = ndctl
> kernel BUG at include/linux/mm.h:1107!
> [c000000274087ba0] c0000000009e3500 devm_action_release+0x30/0x50
> [c000000274087bc0] c0000000009e4758 release_nodes+0x268/0x2d0
> [c000000274087c30] c0000000009dd144 device_release_driver_internal+0x174/0x240
> [c000000274087c70] c0000000009d9dfc unbind_store+0x13c/0x190
> [c000000274087cb0] c0000000009d8a24 drv_attr_store+0x44/0x60
> [c000000274087cd0] c0000000005a7470 sysfs_kf_write+0x70/0xa0
> [c000000274087d10] c0000000005a5cac kernfs_fop_write+0x1ac/0x290
> [c000000274087d60] c0000000004be45c __vfs_write+0x3c/0x70
> [c000000274087d80] c0000000004c26e4 vfs_write+0xe4/0x200
> [c000000274087dd0] c0000000004c2a6c ksys_write+0x7c/0x140
> [c000000274087e20] c00000000000bbd0 system_call+0x5c/0x68
> 
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> [ minimze code changes, rephrase description ]
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memremap.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 557e53c6fb46..8c2fb44c3b4d 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -123,6 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>  void memunmap_pages(struct dev_pagemap *pgmap)
>  {
>  	struct resource *res = &pgmap->res;
> +	struct page *first_page;
>  	unsigned long pfn;
>  	int nid;
>  
> @@ -131,14 +132,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
>  		put_page(pfn_to_page(pfn));
>  	dev_pagemap_cleanup(pgmap);
>  
> +	/* make sure to access a memmap that was actually initialized */
> +	first_page = pfn_to_page(pfn_first(pgmap));
> +
>  	/* pages are dead and unused, undo the arch mapping */
> -	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
> +	nid = page_to_nid(first_page);

Why we need 'nid = page_to_nid(first_page)' we didnt use it anymore in this function ?

>  
>  	mem_hotplug_begin();
>  	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> -		pfn = PHYS_PFN(res->start);
> -		__remove_pages(page_zone(pfn_to_page(pfn)), pfn,
> -				 PHYS_PFN(resource_size(res)), NULL);
> +		__remove_pages(page_zone(first_page), PHYS_PFN(res->start),
> +			       PHYS_PFN(resource_size(res)), NULL);
>  	} else {
>  		arch_remove_memory(nid, res->start, resource_size(res),
>  				pgmap_altmap(pgmap));
> -- 
> 2.21.0
>
Best regards
Damian
 

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Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

[David Hildenbrand]

On 06.10.19 21:58, Damian Tometzki wrote:
> Hello David,
> 
> patch 05/10 is missing in the patch series. 
> 

Hi Damian,

not really. Could be that lkml is slow today. E.g., check

https://marc.info/?l=linux-mm&m=157035222620403&w=2

and especially

https://marc.info/?l=linux-mm&m=157035225120440&w=2

All mails popped up on the mm list.

> 
> On Sun, 06. Oct 10:56, David Hildenbrand wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
>>
>> With an altmap, the memmap falling into the reserved altmap space are
>> not initialized and, therefore, contain a garbage NID and a garbage
>> zone. Make sure to read the NID/zone from a memmap that was initialzed.
>>
>> This fixes a kernel crash that is observed when destroying a namespace:
>>
>> [   81.356173] kernel BUG at include/linux/mm.h:1107!
>> cpu 0x1: Vector: 700 (Program Check) at [c000000274087890]
>>     pc: c0000000004b9728: memunmap_pages+0x238/0x340
>>     lr: c0000000004b9724: memunmap_pages+0x234/0x340
>> ...
>>     pid   = 3669, comm = ndctl
>> kernel BUG at include/linux/mm.h:1107!
>> [c000000274087ba0] c0000000009e3500 devm_action_release+0x30/0x50
>> [c000000274087bc0] c0000000009e4758 release_nodes+0x268/0x2d0
>> [c000000274087c30] c0000000009dd144 device_release_driver_internal+0x174/0x240
>> [c000000274087c70] c0000000009d9dfc unbind_store+0x13c/0x190
>> [c000000274087cb0] c0000000009d8a24 drv_attr_store+0x44/0x60
>> [c000000274087cd0] c0000000005a7470 sysfs_kf_write+0x70/0xa0
>> [c000000274087d10] c0000000005a5cac kernfs_fop_write+0x1ac/0x290
>> [c000000274087d60] c0000000004be45c __vfs_write+0x3c/0x70
>> [c000000274087d80] c0000000004c26e4 vfs_write+0xe4/0x200
>> [c000000274087dd0] c0000000004c2a6c ksys_write+0x7c/0x140
>> [c000000274087e20] c00000000000bbd0 system_call+0x5c/0x68
>>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Jason Gunthorpe <jgg@ziepe.ca>
>> Cc: Logan Gunthorpe <logang@deltatee.com>
>> Cc: Ira Weiny <ira.weiny@intel.com>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> [ minimze code changes, rephrase description ]
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  mm/memremap.c | 11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/memremap.c b/mm/memremap.c
>> index 557e53c6fb46..8c2fb44c3b4d 100644
>> --- a/mm/memremap.c
>> +++ b/mm/memremap.c
>> @@ -123,6 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>>  void memunmap_pages(struct dev_pagemap *pgmap)
>>  {
>>  	struct resource *res = &pgmap->res;
>> +	struct page *first_page;
>>  	unsigned long pfn;
>>  	int nid;
>>  
>> @@ -131,14 +132,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
>>  		put_page(pfn_to_page(pfn));
>>  	dev_pagemap_cleanup(pgmap);
>>  
>> +	/* make sure to access a memmap that was actually initialized */
>> +	first_page = pfn_to_page(pfn_first(pgmap));
>> +
>>  	/* pages are dead and unused, undo the arch mapping */
>> -	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
>> +	nid = page_to_nid(first_page);
> 
> Why we need 'nid = page_to_nid(first_page)' we didnt use it anymore in this function ?

Please see ...

> 
>>  
>>  	mem_hotplug_begin();
>>  	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
>> -		pfn = PHYS_PFN(res->start);
>> -		__remove_pages(page_zone(pfn_to_page(pfn)), pfn,
>> -				 PHYS_PFN(resource_size(res)), NULL);
>> +		__remove_pages(page_zone(first_page), PHYS_PFN(res->start),
>> +			       PHYS_PFN(resource_size(res)), NULL);
>>  	} else {
>>  		arch_remove_memory(nid, res->start, resource_size(res),
                                   ^ here

:)

>>  				pgmap_altmap(pgmap));



-- 

Thanks,

David / dhildenb

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Re: [PATCH v6 01/10] mm/memunmap: Don't access uninitialized memmap in memunmap_pages()

[David Hildenbrand]

On 06.10.19 10:56, David Hildenbrand wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
> 
> With an altmap, the memmap falling into the reserved altmap space are
> not initialized and, therefore, contain a garbage NID and a garbage
> zone. Make sure to read the NID/zone from a memmap that was initialzed.
> 
> This fixes a kernel crash that is observed when destroying a namespace:
> 
> [   81.356173] kernel BUG at include/linux/mm.h:1107!
> cpu 0x1: Vector: 700 (Program Check) at [c000000274087890]
>      pc: c0000000004b9728: memunmap_pages+0x238/0x340
>      lr: c0000000004b9724: memunmap_pages+0x234/0x340
> ...
>      pid   = 3669, comm = ndctl
> kernel BUG at include/linux/mm.h:1107!
> [c000000274087ba0] c0000000009e3500 devm_action_release+0x30/0x50
> [c000000274087bc0] c0000000009e4758 release_nodes+0x268/0x2d0
> [c000000274087c30] c0000000009dd144 device_release_driver_internal+0x174/0x240
> [c000000274087c70] c0000000009d9dfc unbind_store+0x13c/0x190
> [c000000274087cb0] c0000000009d8a24 drv_attr_store+0x44/0x60
> [c000000274087cd0] c0000000005a7470 sysfs_kf_write+0x70/0xa0
> [c000000274087d10] c0000000005a5cac kernfs_fop_write+0x1ac/0x290
> [c000000274087d60] c0000000004be45c __vfs_write+0x3c/0x70
> [c000000274087d80] c0000000004c26e4 vfs_write+0xe4/0x200
> [c000000274087dd0] c0000000004c2a6c ksys_write+0x7c/0x140
> [c000000274087e20] c00000000000bbd0 system_call+0x5c/0x68
> 
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> [ minimze code changes, rephrase description ]
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   mm/memremap.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 557e53c6fb46..8c2fb44c3b4d 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -123,6 +123,7 @@ static void dev_pagemap_cleanup(struct dev_pagemap *pgmap)
>   void memunmap_pages(struct dev_pagemap *pgmap)
>   {
>   	struct resource *res = &pgmap->res;
> +	struct page *first_page;
>   	unsigned long pfn;
>   	int nid;
>   
> @@ -131,14 +132,16 @@ void memunmap_pages(struct dev_pagemap *pgmap)
>   		put_page(pfn_to_page(pfn));
>   	dev_pagemap_cleanup(pgmap);
>   
> +	/* make sure to access a memmap that was actually initialized */
> +	first_page = pfn_to_page(pfn_first(pgmap));
> +
>   	/* pages are dead and unused, undo the arch mapping */
> -	nid = page_to_nid(pfn_to_page(PHYS_PFN(res->start)));
> +	nid = page_to_nid(first_page);
>   
>   	mem_hotplug_begin();
>   	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> -		pfn = PHYS_PFN(res->start);
> -		__remove_pages(page_zone(pfn_to_page(pfn)), pfn,
> -				 PHYS_PFN(resource_size(res)), NULL);
> +		__remove_pages(page_zone(first_page), PHYS_PFN(res->start),
> +			       PHYS_PFN(resource_size(res)), NULL);
>   	} else {
>   		arch_remove_memory(nid, res->start, resource_size(res),
>   				pgmap_altmap(pgmap));
> 

@Andrew, can you add

Fixes: 2c2a5af6fed2 ("mm, memory_hotplug: add nid parameter to 
arch_remove_memory")

(which basically introduced the nid = page_to_nid(first_page))

The "page_zone(pfn_to_page(pfn)" was introduced by 69324b8f4833 ("mm, 
devm_memremap_pages: add MEMORY_DEVICE_PRIVATE support"), however, I 
think we will never have driver reserved memory with 
MEMORY_DEVICE_PRIVATE (no altmap AFAIKS).

Also, I think

Cc: stable@vger.kernel.org # v5.0+

makes sense.

-- 

Thanks,

David / dhildenb

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Re: [PATCH v6 03/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_pgdat_span()

[David Hildenbrand]

On 06.10.19 10:56, David Hildenbrand wrote:
> We might use the nid of memmaps that were never initialized. For
> example, if the memmap was poisoned, we will crash the kernel in
> pfn_to_nid() right now. Let's use the calculated boundaries of the separate
> zones instead. This now also avoids having to iterate over a whole bunch of
> subsections again, after shrinking one zone.
> 
> Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory
> hotplug"), the memmap was initialized to 0 and the node was set to the
> right value. After that commit, the node might be garbage.
> 
> We'll have to fix shrink_zone_span() next.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")

@Andrew, can you convert that to

Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319

and add

Cc: stable@vger.kernel.org # v4.13+

-- 

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David / dhildenb

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Re: [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span()

[David Hildenbrand]

On 06.10.19 10:56, David Hildenbrand wrote:
> Let's limit shrinking to !ZONE_DEVICE so we can fix the current code. We
> should never try to touch the memmap of offline sections where we could
> have uninitialized memmaps and could trigger BUGs when calling
> page_to_nid() on poisoned pages.
> 
> There is no reliable way to distinguish an uninitialized memmap from an
> initialized memmap that belongs to ZONE_DEVICE, as we don't have
> anything like SECTION_IS_ONLINE we can use similar to
> pfn_to_online_section() for !ZONE_DEVICE memory. E.g.,
> set_zone_contiguous() similarly relies on pfn_to_online_section() and
> will therefore never set a ZONE_DEVICE zone consecutive. Stopping to
> shrink the ZONE_DEVICE therefore results in no observable changes,
> besides /proc/zoneinfo indicating different boundaries - something we
> can totally live with.
> 
> Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory
> hotplug"), the memmap was initialized with 0 and the node with the
> right value. So the zone might be wrong but not garbage. After that
> commit, both the zone and the node will be garbage when touching
> uninitialized memmaps.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")

@Andrew, can you convert that to

Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded 
memory to zones until online") # visible after d0dc12e86b319

and add

Cc: stable@vger.kernel.org # v4.13+


-- 

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Re: [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span()

[Andrew Morton]

On Mon, 14 Oct 2019 11:32:13 +0200 David Hildenbrand <david@redhat.com> wrote:

> > Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
> 
> @Andrew, can you convert that to
> 
> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded 
> memory to zones until online") # visible after d0dc12e86b319
> 
> and add
> 
> Cc: stable@vger.kernel.org # v4.13+

Done, thanks.

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Re: [PATCH v6 06/10] mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone()

[David Hildenbrand]

On 06.10.19 10:56, David Hildenbrand wrote:
> Let's poison the pages similar to when adding new memory in
> sparse_add_section(). Also call remove_pfn_range_from_zone() from
> memunmap_pages(), so we can poison the memmap from there as well.
> 
> While at it, calculate the pfn in memunmap_pages() only once.

FWIW, this comment is stale and could be dropped :)

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Re: [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span()

[David Hildenbrand]

On 14.10.19 21:17, Andrew Morton wrote:
> On Mon, 14 Oct 2019 11:32:13 +0200 David Hildenbrand <david@redhat.com> wrote:
> 
>>> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
>>
>> @Andrew, can you convert that to
>>
>> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded
>> memory to zones until online") # visible after d0dc12e86b319
>>
>> and add
>>
>> Cc: stable@vger.kernel.org # v4.13+
> 
> Done, thanks.
> 

Just a note that Toshiki reported a BUG (race between delayed
initialization of ZONE_DEVICE memmaps without holding the memory
hotplug lock and concurrent zone shrinking).

https://lkml.org/lkml/2019/11/14/1040

"Iteration of create and destroy namespace causes the panic as below:

[   41.207694] kernel BUG at mm/page_alloc.c:535!
[   41.208109] invalid opcode: 0000 [#1] SMP PTI
[   41.208508] CPU: 7 PID: 2766 Comm: ndctl Not tainted 5.4.0-rc4 #6
[   41.209064] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
[   41.210175] RIP: 0010:set_pfnblock_flags_mask+0x95/0xf0
[   41.210643] Code: 04 41 83 e2 3c 48 8d 04 a8 48 c1 e0 07 48 03 04 dd e0 59 55 bb 48 8b 58 68 48 39 da 73 0e 48 c7 c6 70 ac 11 bb e8 1b b2 fd ff <0f> 0b 48 03 58 78 48 39 da 73 e9 49 01 ca b9 3f 00 00 00 4f 8d 0c
[   41.212354] RSP: 0018:ffffac0d41557c80 EFLAGS: 00010246
[   41.212821] RAX: 000000000000004a RBX: 0000000000244a00 RCX: 0000000000000000
[   41.213459] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffbb1197dc
[   41.214100] RBP: 000000000000000c R08: 0000000000000439 R09: 0000000000000059
[   41.214736] R10: 0000000000000000 R11: ffffac0d41557b08 R12: ffff8be475ea72b0
[   41.215376] R13: 000000000000fa00 R14: 0000000000250000 R15: 00000000fffc0bb5
[   41.216008] FS:  00007f30862ab600(0000) GS:ffff8be57bc40000(0000) knlGS:0000000000000000
[   41.216771] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   41.217299] CR2: 000055e824d0d508 CR3: 0000000231dac000 CR4: 00000000000006e0
[   41.217934] Call Trace:
[   41.218225]  memmap_init_zone_device+0x165/0x17c
[   41.218642]  memremap_pages+0x4c1/0x540
[   41.218989]  devm_memremap_pages+0x1d/0x60
[   41.219367]  pmem_attach_disk+0x16b/0x600 [nd_pmem]
[   41.219804]  ? devm_nsio_enable+0xb8/0xe0
[   41.220172]  nvdimm_bus_probe+0x69/0x1c0
[   41.220526]  really_probe+0x1c2/0x3e0
[   41.220856]  driver_probe_device+0xb4/0x100
[   41.221238]  device_driver_attach+0x4f/0x60
[   41.221611]  bind_store+0xc9/0x110
[   41.221919]  kernfs_fop_write+0x116/0x190
[   41.222326]  vfs_write+0xa5/0x1a0
[   41.222626]  ksys_write+0x59/0xd0
[   41.222927]  do_syscall_64+0x5b/0x180
[   41.223264]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   41.223714] RIP: 0033:0x7f30865d0ed8
[   41.224037] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 45 78 0d 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
[   41.225920] RSP: 002b:00007fffe5d30a78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[   41.226608] RAX: ffffffffffffffda RBX: 000055e824d07f40 RCX: 00007f30865d0ed8
[   41.227242] RDX: 0000000000000007 RSI: 000055e824d07f40 RDI: 0000000000000004
[   41.227870] RBP: 0000000000000007 R08: 0000000000000007 R09: 0000000000000006
[   41.228753] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
[   41.229419] R13: 00007f30862ab528 R14: 0000000000000001 R15: 000055e824d07f40

While creating a namespace and initializing memmap, if you destroy the namespace
and shrink the zone, it will initialize the memmap outside the zone and
trigger VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page) in
set_pfnblock_flags_mask()."


This BUG is also mitigated by this commit, where we for now stop to
shrink the ZONE_DEVICE zone until we can do it in a safe and clean
way.

-- 

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David / dhildenb


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Re: [PATCH v6 04/10] mm/memory_hotplug: Don't access uninitialized memmaps in shrink_zone_span()

[Andrew Morton]

On Tue, 19 Nov 2019 15:16:22 +0100 David Hildenbrand <david@redhat.com> wrote:

> On 14.10.19 21:17, Andrew Morton wrote:
> > On Mon, 14 Oct 2019 11:32:13 +0200 David Hildenbrand <david@redhat.com> wrote:
> > 
> >>> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
> >>
> >> @Andrew, can you convert that to
> >>
> >> Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded
> >> memory to zones until online") # visible after d0dc12e86b319
> >>
> >> and add
> >>
> >> Cc: stable@vger.kernel.org # v4.13+
> > 
> > Done, thanks.
> > 
> 
> Just a note that Toshiki reported a BUG (race between delayed
> initialization of ZONE_DEVICE memmaps without holding the memory
> hotplug lock and concurrent zone shrinking).
> 
> https://lkml.org/lkml/2019/11/14/1040
> 
> "Iteration of create and destroy namespace causes the panic as below:
> 
> [   41.207694] kernel BUG at mm/page_alloc.c:535!
> [   41.208109] invalid opcode: 0000 [#1] SMP PTI
> [   41.208508] CPU: 7 PID: 2766 Comm: ndctl Not tainted 5.4.0-rc4 #6
> [   41.209064] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
> [   41.210175] RIP: 0010:set_pfnblock_flags_mask+0x95/0xf0
> [   41.210643] Code: 04 41 83 e2 3c 48 8d 04 a8 48 c1 e0 07 48 03 04 dd e0 59 55 bb 48 8b 58 68 48 39 da 73 0e 48 c7 c6 70 ac 11 bb e8 1b b2 fd ff <0f> 0b 48 03 58 78 48 39 da 73 e9 49 01 ca b9 3f 00 00 00 4f 8d 0c
> [   41.212354] RSP: 0018:ffffac0d41557c80 EFLAGS: 00010246
> [   41.212821] RAX: 000000000000004a RBX: 0000000000244a00 RCX: 0000000000000000
> [   41.213459] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffbb1197dc
> [   41.214100] RBP: 000000000000000c R08: 0000000000000439 R09: 0000000000000059
> [   41.214736] R10: 0000000000000000 R11: ffffac0d41557b08 R12: ffff8be475ea72b0
> [   41.215376] R13: 000000000000fa00 R14: 0000000000250000 R15: 00000000fffc0bb5
> [   41.216008] FS:  00007f30862ab600(0000) GS:ffff8be57bc40000(0000) knlGS:0000000000000000
> [   41.216771] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   41.217299] CR2: 000055e824d0d508 CR3: 0000000231dac000 CR4: 00000000000006e0
> [   41.217934] Call Trace:
> [   41.218225]  memmap_init_zone_device+0x165/0x17c
> [   41.218642]  memremap_pages+0x4c1/0x540
> [   41.218989]  devm_memremap_pages+0x1d/0x60
> [   41.219367]  pmem_attach_disk+0x16b/0x600 [nd_pmem]
> [   41.219804]  ? devm_nsio_enable+0xb8/0xe0
> [   41.220172]  nvdimm_bus_probe+0x69/0x1c0
> [   41.220526]  really_probe+0x1c2/0x3e0
> [   41.220856]  driver_probe_device+0xb4/0x100
> [   41.221238]  device_driver_attach+0x4f/0x60
> [   41.221611]  bind_store+0xc9/0x110
> [   41.221919]  kernfs_fop_write+0x116/0x190
> [   41.222326]  vfs_write+0xa5/0x1a0
> [   41.222626]  ksys_write+0x59/0xd0
> [   41.222927]  do_syscall_64+0x5b/0x180
> [   41.223264]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [   41.223714] RIP: 0033:0x7f30865d0ed8
> [   41.224037] Code: 89 02 48 c7 c0 ff ff ff ff eb b3 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 45 78 0d 00 8b 00 85 c0 75 17 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 41 54 49 89 d4 55
> [   41.225920] RSP: 002b:00007fffe5d30a78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> [   41.226608] RAX: ffffffffffffffda RBX: 000055e824d07f40 RCX: 00007f30865d0ed8
> [   41.227242] RDX: 0000000000000007 RSI: 000055e824d07f40 RDI: 0000000000000004
> [   41.227870] RBP: 0000000000000007 R08: 0000000000000007 R09: 0000000000000006
> [   41.228753] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
> [   41.229419] R13: 00007f30862ab528 R14: 0000000000000001 R15: 000055e824d07f40
> 
> While creating a namespace and initializing memmap, if you destroy the namespace
> and shrink the zone, it will initialize the memmap outside the zone and
> trigger VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page) in
> set_pfnblock_flags_mask()."
> 
> 
> This BUG is also mitigated by this commit, where we for now stop to
> shrink the ZONE_DEVICE zone until we can do it in a safe and clean
> way.
> 

OK, thanks.  I updated the changelog, added Reported-by:Toshiki and
shall squeeze this fix into 5.4.


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Re: [PATCH v6 05/10] mm/memory_hotplug: Shrink zones when offlining memory

[David Hildenbrand]

On 03.12.19 16:10, Oscar Salvador wrote:
> On Sun, Oct 06, 2019 at 10:56:41AM +0200, David Hildenbrand wrote:
>> Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> I did not see anything wrong with the taken approach, and makes sense to me.
> The only thing that puzzles me is we seem to not balance spanned_pages
> for ZONE_DEVICE anymore.
> memremap_pages() increments them via move_pfn_range_to_zone, but we skip
> ZONE_DEVICE in remove_pfn_range_from_zone.

Yes, documented e.g., in

commit 7ce700bf11b5e2cb84e4352bbdf2123a7a239c84
Author: David Hildenbrand <david@redhat.com>
Date:   Thu Nov 21 17:53:56 2019 -0800

    mm/memory_hotplug: don't access uninitialized memmaps in
shrink_zone_span()

Needs some more thought - but is definitely not urgent (well, now it's
at least no longer completely broken).

> 
> That is not really related to this patch, so I might be missing something,
> but it caught my eye while reviewing this.
> 
> Anyway, for this one:
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> 

Thanks!

> 
> off-topic: I __think__ we really need to trim the CC list.

Yes we should :) - done.

-- 
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Re: [PATCH v6 06/10] mm/memory_hotplug: Poison memmap in remove_pfn_range_from_zone()

[Oscar Salvador]

On Sun, Oct 06, 2019 at 10:56:42AM +0200, David Hildenbrand wrote:
> Let's poison the pages similar to when adding new memory in
> sparse_add_section(). Also call remove_pfn_range_from_zone() from
> memunmap_pages(), so we can poison the memmap from there as well.
> 
> While at it, calculate the pfn in memunmap_pages() only once.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Looks good to me, it is fine as long as we do not access those pages later on,
and if my eyes did not lie to me, we have to proper checks (pfn_to_online_page)
in place to avoid that, so:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

-- 
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SUSE L3

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Re: [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn

[Oscar Salvador]

On Sun, Oct 06, 2019 at 10:56:43AM +0200, David Hildenbrand wrote:
> With shrink_pgdat_span() out of the way, we now always have a valid
> zone.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Oscar Salvador <osalvador@suse.de>

> ---
>  mm/memory_hotplug.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index bf5173e7913d..f294918f7211 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -337,7 +337,7 @@ static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
>  		if (unlikely(pfn_to_nid(start_pfn) != nid))
>  			continue;
>  
> -		if (zone && zone != page_zone(pfn_to_page(start_pfn)))
> +		if (zone != page_zone(pfn_to_page(start_pfn)))
>  			continue;
>  
>  		return start_pfn;
> @@ -362,7 +362,7 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
>  		if (unlikely(pfn_to_nid(pfn) != nid))
>  			continue;
>  
> -		if (zone && zone != page_zone(pfn_to_page(pfn)))
> +		if (zone != page_zone(pfn_to_page(pfn)))
>  			continue;
>  
>  		return pfn;
> -- 
> 2.21.0
> 

-- 
Oscar Salvador
SUSE L3

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Oscar Salvador]

On Sun, Oct 06, 2019 at 10:56:44AM +0200, David Hildenbrand wrote:
> If we have holes, the holes will automatically get detected and removed
> once we remove the next bigger/smaller section. The extra checks can
> go.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Heh, I have been here before.
I have to confess that when I wrote my version of this I was not really 100%
about removing it, because hotplug was a sort of a "catchall" for all sort of weird
and corner-cases configurations, but thinking more about it, I cannot think of
any situation that would make this blow up.

Reviewed-by: Oscar Salvador <osalvador@suse.de>

> ---
>  mm/memory_hotplug.c | 34 +++++++---------------------------
>  1 file changed, 7 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index f294918f7211..8dafa1ba8d9f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>  		if (pfn) {
>  			zone->zone_start_pfn = pfn;
>  			zone->spanned_pages = zone_end_pfn - pfn;
> +		} else {
> +			zone->zone_start_pfn = 0;
> +			zone->spanned_pages = 0;
>  		}
>  	} else if (zone_end_pfn == end_pfn) {
>  		/*
> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>  					       start_pfn);
>  		if (pfn)
>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
> +		else {
> +			zone->zone_start_pfn = 0;
> +			zone->spanned_pages = 0;
> +		}
>  	}
> -
> -	/*
> -	 * The section is not biggest or smallest mem_section in the zone, it
> -	 * only creates a hole in the zone. So in this case, we need not
> -	 * change the zone. But perhaps, the zone has only hole data. Thus
> -	 * it check the zone has only hole or not.
> -	 */
> -	pfn = zone_start_pfn;
> -	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
> -		if (unlikely(!pfn_to_online_page(pfn)))
> -			continue;
> -
> -		if (page_zone(pfn_to_page(pfn)) != zone)
> -			continue;
> -
> -		/* Skip range to be removed */
> -		if (pfn >= start_pfn && pfn < end_pfn)
> -			continue;
> -
> -		/* If we find valid section, we have nothing to do */
> -		zone_span_writeunlock(zone);
> -		return;
> -	}
> -
> -	/* The zone has no valid section */
> -	zone->zone_start_pfn = 0;
> -	zone->spanned_pages = 0;
>  	zone_span_writeunlock(zone);
>  }
>  
> -- 
> 2.21.0
> 

-- 
Oscar Salvador
SUSE L3

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

On 04.02.20 10:13, Oscar Salvador wrote:
> On Sun, Oct 06, 2019 at 10:56:44AM +0200, David Hildenbrand wrote:
>> If we have holes, the holes will automatically get detected and removed
>> once we remove the next bigger/smaller section. The extra checks can
>> go.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Heh, I have been here before.
> I have to confess that when I wrote my version of this I was not really 100%
> about removing it, because hotplug was a sort of a "catchall" for all sort of weird
> and corner-cases configurations, but thinking more about it, I cannot think of
> any situation that would make this blow up.
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>

Thanks for your review Oscar!

-- 
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David / dhildenb


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Re: [PATCH v6 09/10] mm/memory_hotplug: Drop local variables in shrink_zone_span()

[Oscar Salvador]

On Sun, Oct 06, 2019 at 10:56:45AM +0200, David Hildenbrand wrote:
> Get rid of the unnecessary local variables.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memory_hotplug.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 8dafa1ba8d9f..843481bd507d 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -374,14 +374,11 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
>  static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>  			     unsigned long end_pfn)
>  {
> -	unsigned long zone_start_pfn = zone->zone_start_pfn;
> -	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
> -	unsigned long zone_end_pfn = z;
>  	unsigned long pfn;
>  	int nid = zone_to_nid(zone);

We could also remove the nid, right?
AFAICS, the nid is only used in find_{smallest/biggest}_section_pfn so we could
place there as well.

Anyway, nothing to nit-pick about:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

>  
>  	zone_span_writelock(zone);
> -	if (zone_start_pfn == start_pfn) {
> +	if (zone->zone_start_pfn == start_pfn) {
>  		/*
>  		 * If the section is smallest section in the zone, it need
>  		 * shrink zone->zone_start_pfn and zone->zone_spanned_pages.
> @@ -389,25 +386,25 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>  		 * for shrinking zone.
>  		 */
>  		pfn = find_smallest_section_pfn(nid, zone, end_pfn,
> -						zone_end_pfn);
> +						zone_end_pfn(zone));
>  		if (pfn) {
> +			zone->spanned_pages = zone_end_pfn(zone) - pfn;
>  			zone->zone_start_pfn = pfn;
> -			zone->spanned_pages = zone_end_pfn - pfn;
>  		} else {
>  			zone->zone_start_pfn = 0;
>  			zone->spanned_pages = 0;
>  		}
> -	} else if (zone_end_pfn == end_pfn) {
> +	} else if (zone_end_pfn(zone) == end_pfn) {
>  		/*
>  		 * If the section is biggest section in the zone, it need
>  		 * shrink zone->spanned_pages.
>  		 * In this case, we find second biggest valid mem_section for
>  		 * shrinking zone.
>  		 */
> -		pfn = find_biggest_section_pfn(nid, zone, zone_start_pfn,
> +		pfn = find_biggest_section_pfn(nid, zone, zone->zone_start_pfn,
>  					       start_pfn);
>  		if (pfn)
> -			zone->spanned_pages = pfn - zone_start_pfn + 1;
> +			zone->spanned_pages = pfn - zone->zone_start_pfn + 1;
>  		else {
>  			zone->zone_start_pfn = 0;
>  			zone->spanned_pages = 0;
> -- 
> 2.21.0
> 

-- 
Oscar Salvador
SUSE L3

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Re: [PATCH v6 09/10] mm/memory_hotplug: Drop local variables in shrink_zone_span()

[David Hildenbrand]

On 04.02.20 10:26, Oscar Salvador wrote:
> On Sun, Oct 06, 2019 at 10:56:45AM +0200, David Hildenbrand wrote:
>> Get rid of the unnecessary local variables.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  mm/memory_hotplug.c | 15 ++++++---------
>>  1 file changed, 6 insertions(+), 9 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 8dafa1ba8d9f..843481bd507d 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -374,14 +374,11 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
>>  static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>  			     unsigned long end_pfn)
>>  {
>> -	unsigned long zone_start_pfn = zone->zone_start_pfn;
>> -	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
>> -	unsigned long zone_end_pfn = z;
>>  	unsigned long pfn;
>>  	int nid = zone_to_nid(zone);
> 
> We could also remove the nid, right?
> AFAICS, the nid is only used in find_{smallest/biggest}_section_pfn so we could
> place there as well.


I remember sending a patch on this (which was acked, but not picked up
yet)...


oh, there it is :)

https://lore.kernel.org/linux-mm/20191127174158.28226-1-david@redhat.com/

Thanks!

-- 
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David / dhildenb


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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[Oscar Salvador]

On Sun, Oct 06, 2019 at 10:56:46AM +0200, David Hildenbrand wrote:
> Let's drop the basically unused section stuff and simplify.
> 
> Also, let's use a shorter variant to calculate the number of pages to
> the next section boundary.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

I have to confess that it took me while to wrap around my head
with the new min() change, but looks ok:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

> ---
>  mm/memory_hotplug.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 843481bd507d..2275240cfa10 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -490,25 +490,20 @@ static void __remove_section(unsigned long pfn, unsigned long nr_pages,
>  void __remove_pages(unsigned long pfn, unsigned long nr_pages,
>  		    struct vmem_altmap *altmap)
>  {
> +	const unsigned long end_pfn = pfn + nr_pages;
> +	unsigned long cur_nr_pages;
>  	unsigned long map_offset = 0;
> -	unsigned long nr, start_sec, end_sec;
>  
>  	map_offset = vmem_altmap_offset(altmap);
>  
>  	if (check_pfn_span(pfn, nr_pages, "remove"))
>  		return;
>  
> -	start_sec = pfn_to_section_nr(pfn);
> -	end_sec = pfn_to_section_nr(pfn + nr_pages - 1);
> -	for (nr = start_sec; nr <= end_sec; nr++) {
> -		unsigned long pfns;
> -
> +	for (; pfn < end_pfn; pfn += cur_nr_pages) {
>  		cond_resched();
> -		pfns = min(nr_pages, PAGES_PER_SECTION
> -				- (pfn & ~PAGE_SECTION_MASK));
> -		__remove_section(pfn, pfns, map_offset, altmap);
> -		pfn += pfns;
> -		nr_pages -= pfns;
> +		/* Select all remaining pages up to the next section boundary */
> +		cur_nr_pages = min(end_pfn - pfn, -(pfn | PAGE_SECTION_MASK));
> +		__remove_section(pfn, cur_nr_pages, map_offset, altmap);
>  		map_offset = 0;
>  	}
>  }
> -- 
> 2.21.0
> 
> 

-- 
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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[David Hildenbrand]

On 04.02.20 10:46, Oscar Salvador wrote:
> On Sun, Oct 06, 2019 at 10:56:46AM +0200, David Hildenbrand wrote:
>> Let's drop the basically unused section stuff and simplify.
>>
>> Also, let's use a shorter variant to calculate the number of pages to
>> the next section boundary.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> I have to confess that it took me while to wrap around my head
> with the new min() change, but looks ok:

It's a pattern commonly used in compilers and emulators to calculate the
number of bytes to the next block/alignment. (we're missing a macro
(like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up
with a good name (e.g., SIZE_TO_NEXT_ALIGN) .

-- 
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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[Segher Boessenkool]

On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote:
> On 04.02.20 10:46, Oscar Salvador wrote:
> > I have to confess that it took me while to wrap around my head
> > with the new min() change, but looks ok:
> 
> It's a pattern commonly used in compilers and emulators to calculate the
> number of bytes to the next block/alignment. (we're missing a macro
> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up
> with a good name (e.g., SIZE_TO_NEXT_ALIGN) .

You can just write the easy to understand

  ...  ALIGN_UP(x) - x  ...

which is better *without* having a separate name.  Does that not
generate good machine code for you?


Segher

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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[David Hildenbrand]

On 04.02.20 14:13, Segher Boessenkool wrote:
> On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote:
>> On 04.02.20 10:46, Oscar Salvador wrote:
>>> I have to confess that it took me while to wrap around my head
>>> with the new min() change, but looks ok:
>>
>> It's a pattern commonly used in compilers and emulators to calculate the
>> number of bytes to the next block/alignment. (we're missing a macro
>> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up
>> with a good name (e.g., SIZE_TO_NEXT_ALIGN) .
> 
> You can just write the easy to understand
> 
>   ...  ALIGN_UP(x) - x  ...

you mean

ALIGN_UP(x, PAGES_PER_SECTION) - x

but ...

> 
> which is better *without* having a separate name.  Does that not
> generate good machine code for you?

1. There is no ALIGN_UP. "SECTION_ALIGN_UP(x) - x" would be possible
2. It would be wrong if x is already aligned.

e.g., let's use 4096 for simplicity as we all know that value by heart
(for both x and the block size).

a) -(4096 | -4096) -> 4096

b) #define ALIGN_UP(x, a) ((x + a - 1) & -(a))

ALIGN_UP(4096, 4096) - 4096 -> 0

Not as easy as it seems ...

-- 
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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 10/06/19 at 10:56am, David Hildenbrand wrote:
> If we have holes, the holes will automatically get detected and removed
> once we remove the next bigger/smaller section. The extra checks can
> go.
> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Wei Yang <richardw.yang@linux.intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  mm/memory_hotplug.c | 34 +++++++---------------------------
>  1 file changed, 7 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index f294918f7211..8dafa1ba8d9f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>  		if (pfn) {
>  			zone->zone_start_pfn = pfn;
>  			zone->spanned_pages = zone_end_pfn - pfn;
> +		} else {
> +			zone->zone_start_pfn = 0;
> +			zone->spanned_pages = 0;
>  		}
>  	} else if (zone_end_pfn == end_pfn) {
>  		/*
> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>  					       start_pfn);
>  		if (pfn)
>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
> +		else {
> +			zone->zone_start_pfn = 0;
> +			zone->spanned_pages = 0;

Thinking in which case (zone_start_pfn != start_pfn) and it comes here.

> +		}
>  	}
> -
> -	/*
> -	 * The section is not biggest or smallest mem_section in the zone, it
> -	 * only creates a hole in the zone. So in this case, we need not
> -	 * change the zone. But perhaps, the zone has only hole data. Thus
> -	 * it check the zone has only hole or not.
> -	 */
> -	pfn = zone_start_pfn;
> -	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
> -		if (unlikely(!pfn_to_online_page(pfn)))
> -			continue;
> -
> -		if (page_zone(pfn_to_page(pfn)) != zone)
> -			continue;
> -
> -		/* Skip range to be removed */
> -		if (pfn >= start_pfn && pfn < end_pfn)
> -			continue;
> -
> -		/* If we find valid section, we have nothing to do */
> -		zone_span_writeunlock(zone);
> -		return;
> -	}
> -
> -	/* The zone has no valid section */
> -	zone->zone_start_pfn = 0;
> -	zone->spanned_pages = 0;
>  	zone_span_writeunlock(zone);
>  }
>  
> -- 
> 2.21.0
> 
> 


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

On 04.02.20 15:25, Baoquan He wrote:
> On 10/06/19 at 10:56am, David Hildenbrand wrote:
>> If we have holes, the holes will automatically get detected and removed
>> once we remove the next bigger/smaller section. The extra checks can
>> go.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  mm/memory_hotplug.c | 34 +++++++---------------------------
>>  1 file changed, 7 insertions(+), 27 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index f294918f7211..8dafa1ba8d9f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>  		if (pfn) {
>>  			zone->zone_start_pfn = pfn;
>>  			zone->spanned_pages = zone_end_pfn - pfn;
>> +		} else {
>> +			zone->zone_start_pfn = 0;
>> +			zone->spanned_pages = 0;
>>  		}
>>  	} else if (zone_end_pfn == end_pfn) {
>>  		/*
>> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>  					       start_pfn);
>>  		if (pfn)
>>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
>> +		else {
>> +			zone->zone_start_pfn = 0;
>> +			zone->spanned_pages = 0;
> 
> Thinking in which case (zone_start_pfn != start_pfn) and it comes here.

Could only happen in case the zone_start_pfn would have been "out of the
zone already". If you ask me: unlikely :)

This change at least maintains the same result as before (where the
all-holes check would have caught it).

-- 
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Re: [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn

[Wei Yang]

On Sun, Oct 06, 2019 at 10:56:43AM +0200, David Hildenbrand wrote:
>With shrink_pgdat_span() out of the way, we now always have a valid
>zone.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: David Hildenbrand <david@redhat.com>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>


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Re: [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn

[David Hildenbrand]

On 05.02.20 09:57, Wei Yang wrote:
> On Sun, Oct 06, 2019 at 10:56:43AM +0200, David Hildenbrand wrote:
>> With shrink_pgdat_span() out of the way, we now always have a valid
>> zone.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>

Just FYI, the patches are now upstream, so the rb's can no longer be
applied. (but we can send fixes if we find that something is broken ;)
). Thanks!

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Re: [PATCH v6 07/10] mm/memory_hotplug: We always have a zone in find_(smallest|biggest)_section_pfn

[Wei Yang]

On Wed, Feb 05, 2020 at 09:59:41AM +0100, David Hildenbrand wrote:
>On 05.02.20 09:57, Wei Yang wrote:
>> On Sun, Oct 06, 2019 at 10:56:43AM +0200, David Hildenbrand wrote:
>>> With shrink_pgdat_span() out of the way, we now always have a valid
>>> zone.
>>>
>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>> Cc: Oscar Salvador <osalvador@suse.de>
>>> Cc: David Hildenbrand <david@redhat.com>
>>> Cc: Michal Hocko <mhocko@suse.com>
>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> 
>> Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>
>
>Just FYI, the patches are now upstream, so the rb's can no longer be
>applied. (but we can send fixes if we find that something is broken ;)
>). Thanks!
>

Thanks for reminding. :-)

>-- 
>Thanks,
>
>David / dhildenb

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Wei Yang]

On Sun, Oct 06, 2019 at 10:56:44AM +0200, David Hildenbrand wrote:
>If we have holes, the holes will automatically get detected and removed
>once we remove the next bigger/smaller section. The extra checks can
>go.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: David Hildenbrand <david@redhat.com>
>Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>
>---
> mm/memory_hotplug.c | 34 +++++++---------------------------
> 1 file changed, 7 insertions(+), 27 deletions(-)
>
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index f294918f7211..8dafa1ba8d9f 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> 		if (pfn) {
> 			zone->zone_start_pfn = pfn;
> 			zone->spanned_pages = zone_end_pfn - pfn;
>+		} else {
>+			zone->zone_start_pfn = 0;
>+			zone->spanned_pages = 0;
> 		}
> 	} else if (zone_end_pfn == end_pfn) {
> 		/*
>@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> 					       start_pfn);
> 		if (pfn)
> 			zone->spanned_pages = pfn - zone_start_pfn + 1;
>+		else {
>+			zone->zone_start_pfn = 0;
>+			zone->spanned_pages = 0;
>+		}
> 	}

If it is me, I would like to take out these two similar logic out.

For example:

	if () {
	} else if () {
	} else {
		goto out;
	}


	/* The zone has no valid section */
	if (!pfn) {
			zone->zone_start_pfn = 0;
			zone->spanned_pages = 0;
	}

out:
	zone_span_writeunlock(zone);

Well, this is just my personal taste :-)

>-
>-	/*
>-	 * The section is not biggest or smallest mem_section in the zone, it
>-	 * only creates a hole in the zone. So in this case, we need not
>-	 * change the zone. But perhaps, the zone has only hole data. Thus
>-	 * it check the zone has only hole or not.
>-	 */
>-	pfn = zone_start_pfn;
>-	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
>-		if (unlikely(!pfn_to_online_page(pfn)))
>-			continue;
>-
>-		if (page_zone(pfn_to_page(pfn)) != zone)
>-			continue;
>-
>-		/* Skip range to be removed */
>-		if (pfn >= start_pfn && pfn < end_pfn)
>-			continue;
>-
>-		/* If we find valid section, we have nothing to do */
>-		zone_span_writeunlock(zone);
>-		return;
>-	}
>-
>-	/* The zone has no valid section */
>-	zone->zone_start_pfn = 0;
>-	zone->spanned_pages = 0;
> 	zone_span_writeunlock(zone);
> }
> 
>-- 
>2.21.0

-- 
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Re: [PATCH v6 09/10] mm/memory_hotplug: Drop local variables in shrink_zone_span()

[Wei Yang]

On Sun, Oct 06, 2019 at 10:56:45AM +0200, David Hildenbrand wrote:
>Get rid of the unnecessary local variables.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: David Hildenbrand <david@redhat.com>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>

Looks reasonable.

Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>

>---
> mm/memory_hotplug.c | 15 ++++++---------
> 1 file changed, 6 insertions(+), 9 deletions(-)
>
>diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>index 8dafa1ba8d9f..843481bd507d 100644
>--- a/mm/memory_hotplug.c
>+++ b/mm/memory_hotplug.c
>@@ -374,14 +374,11 @@ static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
> static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> 			     unsigned long end_pfn)
> {
>-	unsigned long zone_start_pfn = zone->zone_start_pfn;
>-	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
>-	unsigned long zone_end_pfn = z;
> 	unsigned long pfn;
> 	int nid = zone_to_nid(zone);
> 
> 	zone_span_writelock(zone);
>-	if (zone_start_pfn == start_pfn) {
>+	if (zone->zone_start_pfn == start_pfn) {
> 		/*
> 		 * If the section is smallest section in the zone, it need
> 		 * shrink zone->zone_start_pfn and zone->zone_spanned_pages.
>@@ -389,25 +386,25 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> 		 * for shrinking zone.
> 		 */
> 		pfn = find_smallest_section_pfn(nid, zone, end_pfn,
>-						zone_end_pfn);
>+						zone_end_pfn(zone));
> 		if (pfn) {
>+			zone->spanned_pages = zone_end_pfn(zone) - pfn;
> 			zone->zone_start_pfn = pfn;
>-			zone->spanned_pages = zone_end_pfn - pfn;
> 		} else {
> 			zone->zone_start_pfn = 0;
> 			zone->spanned_pages = 0;
> 		}
>-	} else if (zone_end_pfn == end_pfn) {
>+	} else if (zone_end_pfn(zone) == end_pfn) {
> 		/*
> 		 * If the section is biggest section in the zone, it need
> 		 * shrink zone->spanned_pages.
> 		 * In this case, we find second biggest valid mem_section for
> 		 * shrinking zone.
> 		 */
>-		pfn = find_biggest_section_pfn(nid, zone, zone_start_pfn,
>+		pfn = find_biggest_section_pfn(nid, zone, zone->zone_start_pfn,
> 					       start_pfn);
> 		if (pfn)
>-			zone->spanned_pages = pfn - zone_start_pfn + 1;
>+			zone->spanned_pages = pfn - zone->zone_start_pfn + 1;
> 		else {
> 			zone->zone_start_pfn = 0;
> 			zone->spanned_pages = 0;
>-- 
>2.21.0

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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[Wei Yang]

On Sun, Oct 06, 2019 at 10:56:46AM +0200, David Hildenbrand wrote:
>Let's drop the basically unused section stuff and simplify.
>
>Also, let's use a shorter variant to calculate the number of pages to
>the next section boundary.
>
>Cc: Andrew Morton <akpm@linux-foundation.org>
>Cc: Oscar Salvador <osalvador@suse.de>
>Cc: Michal Hocko <mhocko@suse.com>
>Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>Cc: Dan Williams <dan.j.williams@intel.com>
>Cc: Wei Yang <richardw.yang@linux.intel.com>
>Signed-off-by: David Hildenbrand <david@redhat.com>

Finally understand the code.

Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 02/04/20 at 03:42pm, David Hildenbrand wrote:
> On 04.02.20 15:25, Baoquan He wrote:
> > On 10/06/19 at 10:56am, David Hildenbrand wrote:
> >> If we have holes, the holes will automatically get detected and removed
> >> once we remove the next bigger/smaller section. The extra checks can
> >> go.
> >>
> >> Cc: Andrew Morton <akpm@linux-foundation.org>
> >> Cc: Oscar Salvador <osalvador@suse.de>
> >> Cc: Michal Hocko <mhocko@suse.com>
> >> Cc: David Hildenbrand <david@redhat.com>
> >> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> >> Cc: Dan Williams <dan.j.williams@intel.com>
> >> Cc: Wei Yang <richardw.yang@linux.intel.com>
> >> Signed-off-by: David Hildenbrand <david@redhat.com>
> >> ---
> >>  mm/memory_hotplug.c | 34 +++++++---------------------------
> >>  1 file changed, 7 insertions(+), 27 deletions(-)
> >>
> >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >> index f294918f7211..8dafa1ba8d9f 100644
> >> --- a/mm/memory_hotplug.c
> >> +++ b/mm/memory_hotplug.c
> >> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >>  		if (pfn) {
> >>  			zone->zone_start_pfn = pfn;
> >>  			zone->spanned_pages = zone_end_pfn - pfn;
> >> +		} else {
> >> +			zone->zone_start_pfn = 0;
> >> +			zone->spanned_pages = 0;
> >>  		}
> >>  	} else if (zone_end_pfn == end_pfn) {
> >>  		/*
> >> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >>  					       start_pfn);
> >>  		if (pfn)
> >>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
> >> +		else {
> >> +			zone->zone_start_pfn = 0;
> >> +			zone->spanned_pages = 0;
> > 
> > Thinking in which case (zone_start_pfn != start_pfn) and it comes here.
> 
> Could only happen in case the zone_start_pfn would have been "out of the
> zone already". If you ask me: unlikely :)

Yeah, I also think it's unlikely to come here.

The 'if (zone_start_pfn == start_pfn)' checking also covers the case
(zone_start_pfn == start_pfn && zone_end_pfn == end_pfn). So this
zone_start_pfn/spanned_pages resetting can be removed to avoid
confusion.


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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[Segher Boessenkool]

On Tue, Feb 04, 2020 at 02:38:51PM +0100, David Hildenbrand wrote:
> On 04.02.20 14:13, Segher Boessenkool wrote:
> > On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote:
> >> It's a pattern commonly used in compilers and emulators to calculate the
> >> number of bytes to the next block/alignment. (we're missing a macro
> >> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up
> >> with a good name (e.g., SIZE_TO_NEXT_ALIGN) .

> > You can just write the easy to understand
> > 
> >   ...  ALIGN_UP(x) - x  ...
> 
> you mean
> 
> ALIGN_UP(x, PAGES_PER_SECTION) - x
> 
> but ...
> 
> > which is better *without* having a separate name.  Does that not
> > generate good machine code for you?
> 
> 1. There is no ALIGN_UP. "SECTION_ALIGN_UP(x) - x" would be possible

Erm, you started it ;-)

> 2. It would be wrong if x is already aligned.
> 
> e.g., let's use 4096 for simplicity as we all know that value by heart
> (for both x and the block size).
> 
> a) -(4096 | -4096) -> 4096
> 
> b) #define ALIGN_UP(x, a) ((x + a - 1) & -(a))
> 
> ALIGN_UP(4096, 4096) - 4096 -> 0
> 
> Not as easy as it seems ...

If you always want to return a number >= 1, it it simply
  ALIGN_UP(x + 1) - x
(and replace 1 by any other minimum size required).  This *also* is
easy to read, without having to have any details (and quirks :-/ )
of those utility functions memorised.


Segher

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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[David Hildenbrand]

On 05.02.20 13:51, Segher Boessenkool wrote:
> On Tue, Feb 04, 2020 at 02:38:51PM +0100, David Hildenbrand wrote:
>> On 04.02.20 14:13, Segher Boessenkool wrote:
>>> On Tue, Feb 04, 2020 at 01:41:06PM +0100, David Hildenbrand wrote:
>>>> It's a pattern commonly used in compilers and emulators to calculate the
>>>> number of bytes to the next block/alignment. (we're missing a macro
>>>> (like we have ALIGN_UP/IS_ALIGNED) for that - but it's hard to come up
>>>> with a good name (e.g., SIZE_TO_NEXT_ALIGN) .
> 
>>> You can just write the easy to understand
>>>
>>>   ...  ALIGN_UP(x) - x  ...
>>
>> you mean
>>
>> ALIGN_UP(x, PAGES_PER_SECTION) - x
>>
>> but ...
>>
>>> which is better *without* having a separate name.  Does that not
>>> generate good machine code for you?
>>
>> 1. There is no ALIGN_UP. "SECTION_ALIGN_UP(x) - x" would be possible
> 
> Erm, you started it ;-)

Yeah, I was thinking in the wrong code base :)

> 
>> 2. It would be wrong if x is already aligned.
>>
>> e.g., let's use 4096 for simplicity as we all know that value by heart
>> (for both x and the block size).
>>
>> a) -(4096 | -4096) -> 4096
>>
>> b) #define ALIGN_UP(x, a) ((x + a - 1) & -(a))
>>
>> ALIGN_UP(4096, 4096) - 4096 -> 0
>>
>> Not as easy as it seems ...
> 
> If you always want to return a number >= 1, it it simply
>   ALIGN_UP(x + 1) - x


I'm sorry to have to correct you again for some corner cases:

ALIGN_UP(1, 4096) - 4096 = 0

Again, not as easy as it seems ...

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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[David Hildenbrand]

> I'm sorry to have to correct you again for some corner cases:
> 
> ALIGN_UP(1, 4096) - 4096 = 0
> 
> Again, not as easy as it seems ...
> 

Eh, wait, I'm messing up things. Will double check :)

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

On 05.02.20 13:43, Baoquan He wrote:
> On 02/04/20 at 03:42pm, David Hildenbrand wrote:
>> On 04.02.20 15:25, Baoquan He wrote:
>>> On 10/06/19 at 10:56am, David Hildenbrand wrote:
>>>> If we have holes, the holes will automatically get detected and removed
>>>> once we remove the next bigger/smaller section. The extra checks can
>>>> go.
>>>>
>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>> Cc: Oscar Salvador <osalvador@suse.de>
>>>> Cc: Michal Hocko <mhocko@suse.com>
>>>> Cc: David Hildenbrand <david@redhat.com>
>>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>> ---
>>>>  mm/memory_hotplug.c | 34 +++++++---------------------------
>>>>  1 file changed, 7 insertions(+), 27 deletions(-)
>>>>
>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>> index f294918f7211..8dafa1ba8d9f 100644
>>>> --- a/mm/memory_hotplug.c
>>>> +++ b/mm/memory_hotplug.c
>>>> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>>>  		if (pfn) {
>>>>  			zone->zone_start_pfn = pfn;
>>>>  			zone->spanned_pages = zone_end_pfn - pfn;
>>>> +		} else {
>>>> +			zone->zone_start_pfn = 0;
>>>> +			zone->spanned_pages = 0;
>>>>  		}
>>>>  	} else if (zone_end_pfn == end_pfn) {
>>>>  		/*
>>>> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>>>  					       start_pfn);
>>>>  		if (pfn)
>>>>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
>>>> +		else {
>>>> +			zone->zone_start_pfn = 0;
>>>> +			zone->spanned_pages = 0;
>>>
>>> Thinking in which case (zone_start_pfn != start_pfn) and it comes here.
>>
>> Could only happen in case the zone_start_pfn would have been "out of the
>> zone already". If you ask me: unlikely :)
> 
> Yeah, I also think it's unlikely to come here.
> 
> The 'if (zone_start_pfn == start_pfn)' checking also covers the case
> (zone_start_pfn == start_pfn && zone_end_pfn == end_pfn). So this
> zone_start_pfn/spanned_pages resetting can be removed to avoid
> confusion.

At least I would find it more confusing without it (or want a comment
explaining why this does not have to be handled and why the !pfn case is
not possible).

Anyhow, that patch is already upstream and I don't consider this high
priority. Thanks :)

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Re: [PATCH v6 10/10] mm/memory_hotplug: Cleanup __remove_pages()

[David Hildenbrand]

On 05.02.20 14:18, David Hildenbrand wrote:
>> I'm sorry to have to correct you again for some corner cases:
>>
>> ALIGN_UP(1, 4096) - 4096 = 0
>>
>> Again, not as easy as it seems ...
>>
> 
> Eh, wait, I'm messing up things. Will double check :)
> 

Yes, makes sense, will send a patch and cc you. Thanks!

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 02/05/20 at 02:20pm, David Hildenbrand wrote:
> On 05.02.20 13:43, Baoquan He wrote:
> > On 02/04/20 at 03:42pm, David Hildenbrand wrote:
> >> On 04.02.20 15:25, Baoquan He wrote:
> >>> On 10/06/19 at 10:56am, David Hildenbrand wrote:
> >>>> If we have holes, the holes will automatically get detected and removed
> >>>> once we remove the next bigger/smaller section. The extra checks can
> >>>> go.
> >>>>
> >>>> Cc: Andrew Morton <akpm@linux-foundation.org>
> >>>> Cc: Oscar Salvador <osalvador@suse.de>
> >>>> Cc: Michal Hocko <mhocko@suse.com>
> >>>> Cc: David Hildenbrand <david@redhat.com>
> >>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> >>>> Cc: Dan Williams <dan.j.williams@intel.com>
> >>>> Cc: Wei Yang <richardw.yang@linux.intel.com>
> >>>> Signed-off-by: David Hildenbrand <david@redhat.com>
> >>>> ---
> >>>>  mm/memory_hotplug.c | 34 +++++++---------------------------
> >>>>  1 file changed, 7 insertions(+), 27 deletions(-)
> >>>>
> >>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >>>> index f294918f7211..8dafa1ba8d9f 100644
> >>>> --- a/mm/memory_hotplug.c
> >>>> +++ b/mm/memory_hotplug.c
> >>>> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >>>>  		if (pfn) {
> >>>>  			zone->zone_start_pfn = pfn;
> >>>>  			zone->spanned_pages = zone_end_pfn - pfn;
> >>>> +		} else {
> >>>> +			zone->zone_start_pfn = 0;
> >>>> +			zone->spanned_pages = 0;
> >>>>  		}
> >>>>  	} else if (zone_end_pfn == end_pfn) {
> >>>>  		/*
> >>>> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >>>>  					       start_pfn);
> >>>>  		if (pfn)
> >>>>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
> >>>> +		else {
> >>>> +			zone->zone_start_pfn = 0;
> >>>> +			zone->spanned_pages = 0;
> >>>
> >>> Thinking in which case (zone_start_pfn != start_pfn) and it comes here.
> >>
> >> Could only happen in case the zone_start_pfn would have been "out of the
> >> zone already". If you ask me: unlikely :)
> > 
> > Yeah, I also think it's unlikely to come here.
> > 
> > The 'if (zone_start_pfn == start_pfn)' checking also covers the case
> > (zone_start_pfn == start_pfn && zone_end_pfn == end_pfn). So this
> > zone_start_pfn/spanned_pages resetting can be removed to avoid
> > confusion.
> 
> At least I would find it more confusing without it (or want a comment
> explaining why this does not have to be handled and why the !pfn case is
> not possible).

I don't get why being w/o it will be more confusing, but it's OK since
it doesn't impact anything. 

> 
> Anyhow, that patch is already upstream and I don't consider this high
> priority. Thanks :)

Yeah, noticed you told Wei the status in another patch thread, I am fine
with it, just leave it to you to decide. Thanks.


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

On 05.02.20 14:34, Baoquan He wrote:
> On 02/05/20 at 02:20pm, David Hildenbrand wrote:
>> On 05.02.20 13:43, Baoquan He wrote:
>>> On 02/04/20 at 03:42pm, David Hildenbrand wrote:
>>>> On 04.02.20 15:25, Baoquan He wrote:
>>>>> On 10/06/19 at 10:56am, David Hildenbrand wrote:
>>>>>> If we have holes, the holes will automatically get detected and removed
>>>>>> once we remove the next bigger/smaller section. The extra checks can
>>>>>> go.
>>>>>>
>>>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
>>>>>> Cc: Oscar Salvador <osalvador@suse.de>
>>>>>> Cc: Michal Hocko <mhocko@suse.com>
>>>>>> Cc: David Hildenbrand <david@redhat.com>
>>>>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>>>>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>>>>> Cc: Wei Yang <richardw.yang@linux.intel.com>
>>>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>>>> ---
>>>>>>  mm/memory_hotplug.c | 34 +++++++---------------------------
>>>>>>  1 file changed, 7 insertions(+), 27 deletions(-)
>>>>>>
>>>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>>>> index f294918f7211..8dafa1ba8d9f 100644
>>>>>> --- a/mm/memory_hotplug.c
>>>>>> +++ b/mm/memory_hotplug.c
>>>>>> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>>>>>  		if (pfn) {
>>>>>>  			zone->zone_start_pfn = pfn;
>>>>>>  			zone->spanned_pages = zone_end_pfn - pfn;
>>>>>> +		} else {
>>>>>> +			zone->zone_start_pfn = 0;
>>>>>> +			zone->spanned_pages = 0;
>>>>>>  		}
>>>>>>  	} else if (zone_end_pfn == end_pfn) {
>>>>>>  		/*
>>>>>> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>>>>>>  					       start_pfn);
>>>>>>  		if (pfn)
>>>>>>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
>>>>>> +		else {
>>>>>> +			zone->zone_start_pfn = 0;
>>>>>> +			zone->spanned_pages = 0;
>>>>>
>>>>> Thinking in which case (zone_start_pfn != start_pfn) and it comes here.
>>>>
>>>> Could only happen in case the zone_start_pfn would have been "out of the
>>>> zone already". If you ask me: unlikely :)
>>>
>>> Yeah, I also think it's unlikely to come here.
>>>
>>> The 'if (zone_start_pfn == start_pfn)' checking also covers the case
>>> (zone_start_pfn == start_pfn && zone_end_pfn == end_pfn). So this
>>> zone_start_pfn/spanned_pages resetting can be removed to avoid
>>> confusion.
>>
>> At least I would find it more confusing without it (or want a comment
>> explaining why this does not have to be handled and why the !pfn case is
>> not possible).
> 
> I don't get why being w/o it will be more confusing, but it's OK since
> it doesn't impact anything. 

Because we could actually BUG_ON(!pfn) here, right? Only having a "if
(pfn)" leaves the reader wondering "why is the other case not handled".

> 
>>
>> Anyhow, that patch is already upstream and I don't consider this high
>> priority. Thanks :)
> 
> Yeah, noticed you told Wei the status in another patch thread, I am fine
> with it, just leave it to you to decide. Thanks.

I am fairly busy right now. Can you send a patch (double-checking and
making this eventually unconditional?). Thanks!

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 02/05/20 at 02:38pm, David Hildenbrand wrote:
> On 05.02.20 14:34, Baoquan He wrote:
> > On 02/05/20 at 02:20pm, David Hildenbrand wrote:
> >> On 05.02.20 13:43, Baoquan He wrote:
> >>> On 02/04/20 at 03:42pm, David Hildenbrand wrote:
> >>>> On 04.02.20 15:25, Baoquan He wrote:
> >>>>> On 10/06/19 at 10:56am, David Hildenbrand wrote:
> >>>>>> If we have holes, the holes will automatically get detected and removed
> >>>>>> once we remove the next bigger/smaller section. The extra checks can
> >>>>>> go.
> >>>>>>
> >>>>>> Cc: Andrew Morton <akpm@linux-foundation.org>
> >>>>>> Cc: Oscar Salvador <osalvador@suse.de>
> >>>>>> Cc: Michal Hocko <mhocko@suse.com>
> >>>>>> Cc: David Hildenbrand <david@redhat.com>
> >>>>>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> >>>>>> Cc: Dan Williams <dan.j.williams@intel.com>
> >>>>>> Cc: Wei Yang <richardw.yang@linux.intel.com>
> >>>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
> >>>>>> ---
> >>>>>>  mm/memory_hotplug.c | 34 +++++++---------------------------
> >>>>>>  1 file changed, 7 insertions(+), 27 deletions(-)
> >>>>>>
> >>>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >>>>>> index f294918f7211..8dafa1ba8d9f 100644
> >>>>>> --- a/mm/memory_hotplug.c
> >>>>>> +++ b/mm/memory_hotplug.c
> >>>>>> @@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >>>>>>  		if (pfn) {
> >>>>>>  			zone->zone_start_pfn = pfn;
> >>>>>>  			zone->spanned_pages = zone_end_pfn - pfn;
> >>>>>> +		} else {
> >>>>>> +			zone->zone_start_pfn = 0;
> >>>>>> +			zone->spanned_pages = 0;
> >>>>>>  		}
> >>>>>>  	} else if (zone_end_pfn == end_pfn) {
> >>>>>>  		/*
> >>>>>> @@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >>>>>>  					       start_pfn);
> >>>>>>  		if (pfn)
> >>>>>>  			zone->spanned_pages = pfn - zone_start_pfn + 1;
> >>>>>> +		else {
> >>>>>> +			zone->zone_start_pfn = 0;
> >>>>>> +			zone->spanned_pages = 0;
> >>>>>
> >>>>> Thinking in which case (zone_start_pfn != start_pfn) and it comes here.
> >>>>
> >>>> Could only happen in case the zone_start_pfn would have been "out of the
> >>>> zone already". If you ask me: unlikely :)
> >>>
> >>> Yeah, I also think it's unlikely to come here.
> >>>
> >>> The 'if (zone_start_pfn == start_pfn)' checking also covers the case
> >>> (zone_start_pfn == start_pfn && zone_end_pfn == end_pfn). So this
> >>> zone_start_pfn/spanned_pages resetting can be removed to avoid
> >>> confusion.
> >>
> >> At least I would find it more confusing without it (or want a comment
> >> explaining why this does not have to be handled and why the !pfn case is
> >> not possible).
> > 
> > I don't get why being w/o it will be more confusing, but it's OK since
> > it doesn't impact anything. 
> 
> Because we could actually BUG_ON(!pfn) here, right? Only having a "if
> (pfn)" leaves the reader wondering "why is the other case not handled".
> 
> > 
> >>
> >> Anyhow, that patch is already upstream and I don't consider this high
> >> priority. Thanks :)
> > 
> > Yeah, noticed you told Wei the status in another patch thread, I am fine
> > with it, just leave it to you to decide. Thanks.
> 
> I am fairly busy right now. Can you send a patch (double-checking and
> making this eventually unconditional?). Thanks!

Understood, sorry about the noise, David. I will think about this.


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

>>>> Anyhow, that patch is already upstream and I don't consider this high
>>>> priority. Thanks :)
>>>
>>> Yeah, noticed you told Wei the status in another patch thread, I am fine
>>> with it, just leave it to you to decide. Thanks.
>>
>> I am fairly busy right now. Can you send a patch (double-checking and
>> making this eventually unconditional?). Thanks!
> 
> Understood, sorry about the noise, David. I will think about this.
> 

No need to excuse, really, I'm very happy about review feedback!

The review of this series happened fairly late. Bad, because it's not
perfect, but good, because no serious stuff was found (so far :) ). If
you also don't have time to look into this, I can put it onto my todo
list, just let me know.

Thanks!

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 02/05/20 at 03:16pm, David Hildenbrand wrote:
> >>>> Anyhow, that patch is already upstream and I don't consider this high
> >>>> priority. Thanks :)
> >>>
> >>> Yeah, noticed you told Wei the status in another patch thread, I am fine
> >>> with it, just leave it to you to decide. Thanks.
> >>
> >> I am fairly busy right now. Can you send a patch (double-checking and
> >> making this eventually unconditional?). Thanks!
> > 
> > Understood, sorry about the noise, David. I will think about this.
> > 
> 
> No need to excuse, really, I'm very happy about review feedback!
> 

Glad to hear it, thanks.

> The review of this series happened fairly late. Bad, because it's not
> perfect, but good, because no serious stuff was found (so far :) ). If
> you also don't have time to look into this, I can put it onto my todo
> list, just let me know.

Both is OK to me, as long as thing is clear to us. I will discuss with
Wei Yang for now. You can post patch anytime if you make one.


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

Hi Wei Yang,

On 02/05/20 at 05:59pm, Wei Yang wrote:
> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >index f294918f7211..8dafa1ba8d9f 100644
> >--- a/mm/memory_hotplug.c
> >+++ b/mm/memory_hotplug.c
> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> > 		if (pfn) {
> > 			zone->zone_start_pfn = pfn;
> > 			zone->spanned_pages = zone_end_pfn - pfn;
> >+		} else {
> >+			zone->zone_start_pfn = 0;
> >+			zone->spanned_pages = 0;
> > 		}
> > 	} else if (zone_end_pfn == end_pfn) {
> > 		/*
> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> > 					       start_pfn);
> > 		if (pfn)
> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
> >+		else {
> >+			zone->zone_start_pfn = 0;
> >+			zone->spanned_pages = 0;
> >+		}
> > 	}
> 
> If it is me, I would like to take out these two similar logic out.

I also like this style. 
> 
> For example:
> 
> 	if () {
> 	} else if () {
> 	} else {
> 		goto out;
Here the last else is unnecessary, right?

> 	}
> 
> 

Like this, I believe both David and I will be satisfactory. Even though
I still think his 2nd resetting is not needed :-)

> 	/* The zone has no valid section */
> 	if (!pfn) {
> 			zone->zone_start_pfn = 0;
> 			zone->spanned_pages = 0;
> 	}
> 
> out:
> 	zone_span_writeunlock(zone);
> 
> Well, this is just my personal taste :-)
> 
> >-
> >-	/*
> >-	 * The section is not biggest or smallest mem_section in the zone, it
> >-	 * only creates a hole in the zone. So in this case, we need not
> >-	 * change the zone. But perhaps, the zone has only hole data. Thus
> >-	 * it check the zone has only hole or not.
> >-	 */
> >-	pfn = zone_start_pfn;
> >-	for (; pfn < zone_end_pfn; pfn += PAGES_PER_SUBSECTION) {
> >-		if (unlikely(!pfn_to_online_page(pfn)))
> >-			continue;
> >-
> >-		if (page_zone(pfn_to_page(pfn)) != zone)
> >-			continue;
> >-
> >-		/* Skip range to be removed */
> >-		if (pfn >= start_pfn && pfn < end_pfn)
> >-			continue;
> >-
> >-		/* If we find valid section, we have nothing to do */
> >-		zone_span_writeunlock(zone);
> >-		return;
> >-	}
> >-
> >-	/* The zone has no valid section */
> >-	zone->zone_start_pfn = 0;
> >-	zone->spanned_pages = 0;
> > 	zone_span_writeunlock(zone);
> > }
> > 
> >-- 
> >2.21.0
> 
> -- 
> Wei Yang
> Help you, Help me
> 


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RE: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Laight]

From: Wei Yang
> Sent: 05 February 2020 09:59
...
> If it is me, I would like to take out these two similar logic out.
> 
> For example:
> 
> 	if () {
> 	} else if () {
> 	} else {
> 		goto out;
> 	}

I'm pretty sure the kernel layout rules disallow 'else if'.
It is also pretty horrid unless the conditionals are all related
(so it is almost a switch statement).

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[David Hildenbrand]

On 05.02.20 15:54, David Laight wrote:
> From: Wei Yang
>> Sent: 05 February 2020 09:59
> ...
>> If it is me, I would like to take out these two similar logic out.
>>
>> For example:
>>
>> 	if () {
>> 	} else if () {
>> 	} else {
>> 		goto out;
>> 	}
> 
> I'm pretty sure the kernel layout rules disallow 'else if'.

Huh?

git grep "else if" | wc -l
49336

I'm afraid I don't get what you mean :)

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Wei Yang]

On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
>Hi Wei Yang,
>
>On 02/05/20 at 05:59pm, Wei Yang wrote:
>> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> >index f294918f7211..8dafa1ba8d9f 100644
>> >--- a/mm/memory_hotplug.c
>> >+++ b/mm/memory_hotplug.c
>> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> > 		if (pfn) {
>> > 			zone->zone_start_pfn = pfn;
>> > 			zone->spanned_pages = zone_end_pfn - pfn;
>> >+		} else {
>> >+			zone->zone_start_pfn = 0;
>> >+			zone->spanned_pages = 0;
>> > 		}
>> > 	} else if (zone_end_pfn == end_pfn) {
>> > 		/*
>> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> > 					       start_pfn);
>> > 		if (pfn)
>> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
>> >+		else {
>> >+			zone->zone_start_pfn = 0;
>> >+			zone->spanned_pages = 0;
>> >+		}
>> > 	}
>> 
>> If it is me, I would like to take out these two similar logic out.
>
>I also like this style. 
>> 
>> For example:
>> 
>> 	if () {
>> 	} else if () {
>> 	} else {
>> 		goto out;
>Here the last else is unnecessary, right?
>

I am afraid not.

If the range is not the first or last, we would leave pfn not initialized.


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 02/06/20 at 06:56am, Wei Yang wrote:
> On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
> >Hi Wei Yang,
> >
> >On 02/05/20 at 05:59pm, Wei Yang wrote:
> >> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >> >index f294918f7211..8dafa1ba8d9f 100644
> >> >--- a/mm/memory_hotplug.c
> >> >+++ b/mm/memory_hotplug.c
> >> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >> > 		if (pfn) {
> >> > 			zone->zone_start_pfn = pfn;
> >> > 			zone->spanned_pages = zone_end_pfn - pfn;
> >> >+		} else {
> >> >+			zone->zone_start_pfn = 0;
> >> >+			zone->spanned_pages = 0;
> >> > 		}
> >> > 	} else if (zone_end_pfn == end_pfn) {
> >> > 		/*
> >> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >> > 					       start_pfn);
> >> > 		if (pfn)
> >> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
> >> >+		else {
> >> >+			zone->zone_start_pfn = 0;
> >> >+			zone->spanned_pages = 0;
> >> >+		}
> >> > 	}
> >> 
> >> If it is me, I would like to take out these two similar logic out.
> >
> >I also like this style. 
> >> 
> >> For example:
> >> 
> >> 	if () {
> >> 	} else if () {
> >> 	} else {
> >> 		goto out;
> >Here the last else is unnecessary, right?
> >
> 
> I am afraid not.
> 
> If the range is not the first or last, we would leave pfn not initialized.

Ah, you are right. I forgot that one. Then pfn can be assigned the
zone_start_pfn as the old code. Then the following logic is the same
as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() 
have done the iteration the old for loop was doing.

	unsigned long pfn = zone_start_pfn;	
	if () {
	} else if () {
	} 

	/* The zone has no valid section */
	if (!pfn) {
        	zone->zone_start_pfn = 0;
        	zone->spanned_pages = 0;
	}


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Wei Yang]

On Thu, Feb 06, 2020 at 07:08:26AM +0800, Baoquan He wrote:
>On 02/06/20 at 06:56am, Wei Yang wrote:
>> On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
>> >Hi Wei Yang,
>> >
>> >On 02/05/20 at 05:59pm, Wei Yang wrote:
>> >> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> >> >index f294918f7211..8dafa1ba8d9f 100644
>> >> >--- a/mm/memory_hotplug.c
>> >> >+++ b/mm/memory_hotplug.c
>> >> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> >> > 		if (pfn) {
>> >> > 			zone->zone_start_pfn = pfn;
>> >> > 			zone->spanned_pages = zone_end_pfn - pfn;
>> >> >+		} else {
>> >> >+			zone->zone_start_pfn = 0;
>> >> >+			zone->spanned_pages = 0;
>> >> > 		}
>> >> > 	} else if (zone_end_pfn == end_pfn) {
>> >> > 		/*
>> >> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> >> > 					       start_pfn);
>> >> > 		if (pfn)
>> >> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
>> >> >+		else {
>> >> >+			zone->zone_start_pfn = 0;
>> >> >+			zone->spanned_pages = 0;
>> >> >+		}
>> >> > 	}
>> >> 
>> >> If it is me, I would like to take out these two similar logic out.
>> >
>> >I also like this style. 
>> >> 
>> >> For example:
>> >> 
>> >> 	if () {
>> >> 	} else if () {
>> >> 	} else {
>> >> 		goto out;
>> >Here the last else is unnecessary, right?
>> >
>> 
>> I am afraid not.
>> 
>> If the range is not the first or last, we would leave pfn not initialized.
>
>Ah, you are right. I forgot that one. Then pfn can be assigned the
>zone_start_pfn as the old code. Then the following logic is the same
>as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() 
>have done the iteration the old for loop was doing.
>
>	unsigned long pfn = zone_start_pfn;	
>	if () {
>	} else if () {
>	} 
>
>	/* The zone has no valid section */
>	if (!pfn) {
>        	zone->zone_start_pfn = 0;
>        	zone->spanned_pages = 0;
>	}

This one look better :-)

Thanks

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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Baoquan He]

On 02/06/20 at 07:26am, Wei Yang wrote:
> On Thu, Feb 06, 2020 at 07:08:26AM +0800, Baoquan He wrote:
> >On 02/06/20 at 06:56am, Wei Yang wrote:
> >> On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
> >> >Hi Wei Yang,
> >> >
> >> >On 02/05/20 at 05:59pm, Wei Yang wrote:
> >> >> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> >> >> >index f294918f7211..8dafa1ba8d9f 100644
> >> >> >--- a/mm/memory_hotplug.c
> >> >> >+++ b/mm/memory_hotplug.c
> >> >> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >> >> > 		if (pfn) {
> >> >> > 			zone->zone_start_pfn = pfn;
> >> >> > 			zone->spanned_pages = zone_end_pfn - pfn;
> >> >> >+		} else {
> >> >> >+			zone->zone_start_pfn = 0;
> >> >> >+			zone->spanned_pages = 0;
> >> >> > 		}
> >> >> > 	} else if (zone_end_pfn == end_pfn) {
> >> >> > 		/*
> >> >> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
> >> >> > 					       start_pfn);
> >> >> > 		if (pfn)
> >> >> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
> >> >> >+		else {
> >> >> >+			zone->zone_start_pfn = 0;
> >> >> >+			zone->spanned_pages = 0;
> >> >> >+		}
> >> >> > 	}
> >> >> 
> >> >> If it is me, I would like to take out these two similar logic out.
> >> >
> >> >I also like this style. 
> >> >> 
> >> >> For example:
> >> >> 
> >> >> 	if () {
> >> >> 	} else if () {
> >> >> 	} else {
> >> >> 		goto out;
> >> >Here the last else is unnecessary, right?
> >> >
> >> 
> >> I am afraid not.
> >> 
> >> If the range is not the first or last, we would leave pfn not initialized.
> >
> >Ah, you are right. I forgot that one. Then pfn can be assigned the
> >zone_start_pfn as the old code. Then the following logic is the same
> >as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() 
> >have done the iteration the old for loop was doing.
> >
> >	unsigned long pfn = zone_start_pfn;	
> >	if () {
> >	} else if () {
> >	} 
> >
> >	/* The zone has no valid section */
> >	if (!pfn) {
> >        	zone->zone_start_pfn = 0;
> >        	zone->spanned_pages = 0;
> >	}
> 
> This one look better :-)

Thanks for your confirmation, I will make one patch like this and post.


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Re: [PATCH v6 08/10] mm/memory_hotplug: Don't check for "all holes" in shrink_zone_span()

[Wei Yang]

On Thu, Feb 06, 2020 at 07:30:51AM +0800, Baoquan He wrote:
>On 02/06/20 at 07:26am, Wei Yang wrote:
>> On Thu, Feb 06, 2020 at 07:08:26AM +0800, Baoquan He wrote:
>> >On 02/06/20 at 06:56am, Wei Yang wrote:
>> >> On Wed, Feb 05, 2020 at 10:48:11PM +0800, Baoquan He wrote:
>> >> >Hi Wei Yang,
>> >> >
>> >> >On 02/05/20 at 05:59pm, Wei Yang wrote:
>> >> >> >diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> >> >> >index f294918f7211..8dafa1ba8d9f 100644
>> >> >> >--- a/mm/memory_hotplug.c
>> >> >> >+++ b/mm/memory_hotplug.c
>> >> >> >@@ -393,6 +393,9 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> >> >> > 		if (pfn) {
>> >> >> > 			zone->zone_start_pfn = pfn;
>> >> >> > 			zone->spanned_pages = zone_end_pfn - pfn;
>> >> >> >+		} else {
>> >> >> >+			zone->zone_start_pfn = 0;
>> >> >> >+			zone->spanned_pages = 0;
>> >> >> > 		}
>> >> >> > 	} else if (zone_end_pfn == end_pfn) {
>> >> >> > 		/*
>> >> >> >@@ -405,34 +408,11 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
>> >> >> > 					       start_pfn);
>> >> >> > 		if (pfn)
>> >> >> > 			zone->spanned_pages = pfn - zone_start_pfn + 1;
>> >> >> >+		else {
>> >> >> >+			zone->zone_start_pfn = 0;
>> >> >> >+			zone->spanned_pages = 0;
>> >> >> >+		}
>> >> >> > 	}
>> >> >> 
>> >> >> If it is me, I would like to take out these two similar logic out.
>> >> >
>> >> >I also like this style. 
>> >> >> 
>> >> >> For example:
>> >> >> 
>> >> >> 	if () {
>> >> >> 	} else if () {
>> >> >> 	} else {
>> >> >> 		goto out;
>> >> >Here the last else is unnecessary, right?
>> >> >
>> >> 
>> >> I am afraid not.
>> >> 
>> >> If the range is not the first or last, we would leave pfn not initialized.
>> >
>> >Ah, you are right. I forgot that one. Then pfn can be assigned the
>> >zone_start_pfn as the old code. Then the following logic is the same
>> >as the original code, find_smallest_section_pfn()/find_biggest_section_pfn() 
>> >have done the iteration the old for loop was doing.
>> >
>> >	unsigned long pfn = zone_start_pfn;	
>> >	if () {
>> >	} else if () {
>> >	} 
>> >
>> >	/* The zone has no valid section */
>> >	if (!pfn) {
>> >        	zone->zone_start_pfn = 0;
>> >        	zone->spanned_pages = 0;
>> >	}
>> 
>> This one look better :-)
>
>Thanks for your confirmation, I will make one patch like this and post.

Sure :-)

-- 
Wei Yang
Help you, Help me

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