On Thu, Nov 26, 2020 at 11:05:14AM +0100, David Hildenbrand wrote:
> On 26.11.20 10:36, Mike Rapoport wrote:
> > On Wed, Nov 25, 2020 at 04:38:16PM -0500, Andrea Arcangeli wrote:
> >
> >> At best memory.reserved should be calculated automatically by the
> >> page_alloc.c based on the zone_start_pfn/zone_end_pfn and not passed
> >> by the e820 caller, instead of adding the memory_reserve call for type
> >> 20 we should delete the memory_reserve function.
> >
> > memory.reserved cannot be calculated automatically. It represents all
> > the memory allocations made before page allocator is up. And as
> > memblock_reserve() is the most basic to allocate memory early at boot we
> > cannot really delete it ;-)
> >
> > As for e820 and type 20, unless it is in memblock, page_alloc.c has no
> > way to properly initialize memmap for it. It can continue to guess, like
> > it does with init_unavailable_memory().
>
> AFAIS, init_unavailable_mem() has to logic to setup *any* such struct
> page properly up - except the node/zid, because that's unknown at that
> time. It is documented that (big comment above init_unavailable_mem())
// The comment is a bit inaccurate, but that's another story :)
> which pages won't get initialized again. They *are* initialized, just
> the node/zone is "fake" - that's the real problem we seem to have.
Let's try to merge init_unavailable_memory() into memmap_init().
Than it'll be able to set zone/nid for those nasty pfns that BIOS
decided to keep to itself, like in Andrea's case and will also take care
of struct pages that do not really have a frame in DRAM, but are there
because of arbitrary section size.
Something like this:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index eaa227a479e4..072e94042a11 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6185,24 +6185,84 @@ static void __meminit zone_init_free_lists(struct zone *zone)
}
}
-void __meminit __weak memmap_init(unsigned long size, int nid,
- unsigned long zone,
- unsigned long range_start_pfn)
+#if !defined(CONFIG_FLAT_NODE_MEM_MAP)
+/*
+ * Only struct pages that are backed by physical memory available to the
+ * kernel are zeroed and initialized by memmap_init_zone().
+ * But, there are some struct pages that are either reserved by firmware or
+ * do not correspond to physical page frames becuase actual memory bank is
+ * not a multiple of SECTION_SIZE. Fields of those struct pages may be
+ * accessed (for example page_to_pfn() on some configuration accesses
+ * flags) so we must explicitly initialize those struct pages.
+ */
+static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn,
+ int zone, int node)
{
- unsigned long start_pfn, end_pfn;
+ unsigned long pfn;
+ u64 pgcnt = 0;
+
+ for (pfn = spfn; pfn < epfn; pfn++) {
+ if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
+ pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
+ + pageblock_nr_pages - 1;
+ continue;
+ }
+ __init_single_page(pfn_to_page(pfn), pfn, zone, node);
+ __SetPageReserved(pfn_to_page(pfn));
+ pgcnt++;
+ }
+
+ return pgcnt;
+}
+#else
+static inline u64 init_unavailable_range(unsigned long spfn, unsigned long epfn,
+ int zone, int node)
+{
+ return 0;
+}
+#endif
+
+void __init __weak memmap_init(unsigned long size, int nid,
+ unsigned long zone,
+ unsigned long range_start_pfn)
+{
+ unsigned long start_pfn, end_pfn, next_pfn = 0;
unsigned long range_end_pfn = range_start_pfn + size;
+ u64 pgcnt = 0;
int i;
for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
start_pfn = clamp(start_pfn, range_start_pfn, range_end_pfn);
end_pfn = clamp(end_pfn, range_start_pfn, range_end_pfn);
+ next_pfn = clamp(next_pfn, range_start_pfn, range_end_pfn);
if (end_pfn > start_pfn) {
size = end_pfn - start_pfn;
memmap_init_zone(size, nid, zone, start_pfn,
MEMINIT_EARLY, NULL, MIGRATE_MOVABLE);
}
+
+ if (next_pfn < start_pfn)
+ pgcnt += init_unavailable_range(next_pfn, start_pfn,
+ zone, nid);
+ next_pfn = end_pfn;
}
+
+ /*
+ * Early sections always have a fully populated memmap for the whole
+ * section - see pfn_valid(). If the last section has holes at the
+ * end and that section is marked "online", the memmap will be
+ * considered initialized. Make sure that memmap has a well defined
+ * state.
+ */
+ if (next_pfn < range_end_pfn)
+ pgcnt += init_unavailable_range(next_pfn, range_end_pfn,
+ zone, nid);
+
+ if (pgcnt)
+ pr_info("%s: Zeroed struct page in unavailable ranges: %lld\n",
+ zone_names[zone], pgcnt);
+
}
static int zone_batchsize(struct zone *zone)
@@ -6995,88 +7055,6 @@ void __init free_area_init_memoryless_node(int nid)
free_area_init_node(nid);
}
-#if !defined(CONFIG_FLAT_NODE_MEM_MAP)
-/*
- * Initialize all valid struct pages in the range [spfn, epfn) and mark them
- * PageReserved(). Return the number of struct pages that were initialized.
- */
-static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn)
-{
- unsigned long pfn;
- u64 pgcnt = 0;
-
- for (pfn = spfn; pfn < epfn; pfn++) {
- if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
- pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
- + pageblock_nr_pages - 1;
- continue;
- }
- /*
- * Use a fake node/zone (0) for now. Some of these pages
- * (in memblock.reserved but not in memblock.memory) will
- * get re-initialized via reserve_bootmem_region() later.
- */
- __init_single_page(pfn_to_page(pfn), pfn, 0, 0);
- __SetPageReserved(pfn_to_page(pfn));
- pgcnt++;
- }
-
- return pgcnt;
-}
-
-/*
- * Only struct pages that are backed by physical memory are zeroed and
- * initialized by going through __init_single_page(). But, there are some
- * struct pages which are reserved in memblock allocator and their fields
- * may be accessed (for example page_to_pfn() on some configuration accesses
- * flags). We must explicitly initialize those struct pages.
- *
- * This function also addresses a similar issue where struct pages are left
- * uninitialized because the physical address range is not covered by
- * memblock.memory or memblock.reserved. That could happen when memblock
- * layout is manually configured via memmap=, or when the highest physical
- * address (max_pfn) does not end on a section boundary.
- */
-static void __init init_unavailable_mem(void)
-{
- phys_addr_t start, end;
- u64 i, pgcnt;
- phys_addr_t next = 0;
-
- /*
- * Loop through unavailable ranges not covered by memblock.memory.
- */
- pgcnt = 0;
- for_each_mem_range(i, &start, &end) {
- if (next < start)
- pgcnt += init_unavailable_range(PFN_DOWN(next),
- PFN_UP(start));
- next = end;
- }
-
- /*
- * Early sections always have a fully populated memmap for the whole
- * section - see pfn_valid(). If the last section has holes at the
- * end and that section is marked "online", the memmap will be
- * considered initialized. Make sure that memmap has a well defined
- * state.
- */
- pgcnt += init_unavailable_range(PFN_DOWN(next),
- round_up(max_pfn, PAGES_PER_SECTION));
-
- /*
- * Struct pages that do not have backing memory. This could be because
- * firmware is using some of this memory, or for some other reasons.
- */
- if (pgcnt)
- pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
-}
-#else
-static inline void __init init_unavailable_mem(void)
-{
-}
-#endif /* !CONFIG_FLAT_NODE_MEM_MAP */
-
#if MAX_NUMNODES > 1
/*
* Figure out the number of possible node ids.
@@ -7500,7 +7478,6 @@ void __init free_area_init(unsigned long *max_zone_pfn)
/* Initialise every node */
mminit_verify_pageflags_layout();
setup_nr_node_ids();
- init_unavailable_mem();
for_each_online_node(nid) {
pg_data_t *pgdat = NODE_DATA(nid);
free_area_init_node(nid);
> I agree that this is sub-optimal, as such pages are impossible to detect
> (PageReserved is just not clear as discussed with Andrea). The basic
> question is how we want to proceed:
>
> a) Make sure any online struct page has a valid nid/zid, and is spanned
> by the nid/zid.
> b) Use a fake nid that will bail out when used for page_zone() and
> page_pgdat(), and make pfn walkers detect that.
>
> AFAIU, Andrea seems to prefer a). I thing b) might be easier in corner
> cases. Thoughts?
I'd also prefer (a).
The hardware defines what physical addresses correspond to which node,
so for any populated DIMM (or soldered DRAM for that matter) we can
detect page <-> node relationship.
As for the struct pages that just "hang" in the end of a section (your
example with 4000M), the addresses of these pages still obey the same
rules, so again, we have page <-> node correspondence.
The zones are software construct but they also correspond to some
hardware defined restrictions - each zone has a maximal PFN that HW
allows. Here again we can always know which zone spans that or another
page.
We'd have to fix a couple of things to get there, though :)
> ---
>
> The tricky thing for b) is to fix all call places that do a
> page_zone()/page_pgdat() without checking if they are allowed to do so.
> We would have to audit all callers of page_zone() / page_zone_id() /
> page_pgdat() ...
>
>
> E.g., using a pattern like
> mm/memory_hotplug.c:find_biggest_section_pfn() is fine
>
>
> if (unlikely(!pfn_to_online_page(pfn)))
> continue;
> if (unlikely(pfn_to_nid(pfn) != nid))
> continue;
>
>
> e.g., mm/page_alloc.c:__pageblock_pfn_to_page() would have to be adjusted
>
> start_page = pfn_to_online_page(start_pfn);
> if (!start_page)
> return NULL;
>
> // necessary to avoid ...
> if (page_to_nid(page) == NODE_INVALID)
> return NULL;
>
> // page_zone() from bailing out
> if (page_zone(start_page) != zone)
> return NULL;
>
> --
> Thanks,
>
> David / dhildenb
>
--
Sincerely yours,
Mike.
