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SubjectRe: [PATCH 2/2] mm: zero remaining unavailable struct pages
Date
On 8/23/18 2:25 PM, Masayoshi Mizuma wrote:
> From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>
> There is a kernel panic that is triggered when reading /proc/kpageflags
> on the kernel booted with kernel parameter 'memmap=nn[KMG]!ss[KMG]':
>
> BUG: unable to handle kernel paging request at fffffffffffffffe
> PGD 9b20e067 P4D 9b20e067 PUD 9b210067 PMD 0
> Oops: 0000 [#1] SMP PTI
> CPU: 2 PID: 1728 Comm: page-types Not tainted 4.17.0-rc6-mm1-v4.17-rc6-180605-0816-00236-g2dfb086ef02c+ #160
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.fc28 04/01/2014
> RIP: 0010:stable_page_flags+0x27/0x3c0
> Code: 00 00 00 0f 1f 44 00 00 48 85 ff 0f 84 a0 03 00 00 41 54 55 49 89 fc 53 48 8b 57 08 48 8b 2f 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 01 0f 84 10 03 00 00 31 db 49 8b 54 24 08 4c 89 e7
> RSP: 0018:ffffbbd44111fde0 EFLAGS: 00010202
> RAX: fffffffffffffffe RBX: 00007fffffffeff9 RCX: 0000000000000000
> RDX: 0000000000000001 RSI: 0000000000000202 RDI: ffffed1182fff5c0
> RBP: ffffffffffffffff R08: 0000000000000001 R09: 0000000000000001
> R10: ffffbbd44111fed8 R11: 0000000000000000 R12: ffffed1182fff5c0
> R13: 00000000000bffd7 R14: 0000000002fff5c0 R15: ffffbbd44111ff10
> FS: 00007efc4335a500(0000) GS:ffff93a5bfc00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: fffffffffffffffe CR3: 00000000b2a58000 CR4: 00000000001406e0
> Call Trace:
> kpageflags_read+0xc7/0x120
> proc_reg_read+0x3c/0x60
> __vfs_read+0x36/0x170
> vfs_read+0x89/0x130
> ksys_pread64+0x71/0x90
> do_syscall_64+0x5b/0x160
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7efc42e75e23
> Code: 09 00 ba 9f 01 00 00 e8 ab 81 f4 ff 66 2e 0f 1f 84 00 00 00 00 00 90 83 3d 29 0a 2d 00 00 75 13 49 89 ca b8 11 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 34 c3 48 83 ec 08 e8 db d3 01 00 48 89 04 24
>
> According to kernel bisection, this problem became visible due to commit
> f7f99100d8d9 which changes how struct pages are initialized.
>
> Memblock layout affects the pfn ranges covered by node/zone. Consider
> that we have a VM with 2 NUMA nodes and each node has 4GB memory, and
> the default (no memmap= given) memblock layout is like below:
>
> MEMBLOCK configuration:
> memory size = 0x00000001fff75c00 reserved size = 0x000000000300c000
> memory.cnt = 0x4
> memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0
> memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0
> memory[0x2] [0x0000000100000000-0x000000013fffffff], 0x0000000040000000 bytes on node 0 flags: 0x0
> memory[0x3] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0
> ...
>
> If you give memmap=1G!4G (so it just covers memory[0x2]),
> the range [0x100000000-0x13fffffff] is gone:
>
> MEMBLOCK configuration:
> memory size = 0x00000001bff75c00 reserved size = 0x000000000300c000
> memory.cnt = 0x3
> memory[0x0] [0x0000000000001000-0x000000000009efff], 0x000000000009e000 bytes on node 0 flags: 0x0
> memory[0x1] [0x0000000000100000-0x00000000bffd6fff], 0x00000000bfed7000 bytes on node 0 flags: 0x0
> memory[0x2] [0x0000000140000000-0x000000023fffffff], 0x0000000100000000 bytes on node 1 flags: 0x0
> ...
>
> This causes shrinking node 0's pfn range because it is calculated by
> the address range of memblock.memory. So some of struct pages in the
> gap range are left uninitialized.
>
> We have a function zero_resv_unavail() which does zeroing the struct
> pages outside memblock.memory, but currently it covers only the reserved
> unavailable range (i.e. memblock.memory && !memblock.reserved).
> This patch extends it to cover all unavailable range, which fixes
> the reported issue.
>
> Fixes: f7f99100d8d9 ("mm: stop zeroing memory during allocation in vmemmap")
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Tested-by: Oscar Salvador <osalvador@suse.de>
> Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>

Also, please review and add the following patch to this series:

From 6d23e66e979244734a06c1b636742c2568121b39 Mon Sep 17 00:00:00 2001
From: Pavel Tatashin <pavel.tatashin@microsoft.com>
Date: Mon, 27 Aug 2018 19:10:35 -0400
Subject: [PATCH] mm: return zero_resv_unavail optimization

When checking for valid pfns in zero_resv_unavail(), it is not necessary to
verify that pfns within pageblock_nr_pages ranges are valid, only the first
one needs to be checked. This is because memory for pages are allocated in
contiguous chunks that contain pageblock_nr_pages struct pages.

Signed-off-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
---
mm/page_alloc.c | 46 ++++++++++++++++++++++++++--------------------
1 file changed, 26 insertions(+), 20 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 650d8f16a67e..5dfc206db40e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6441,6 +6441,29 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
}

#if defined(CONFIG_HAVE_MEMBLOCK) && !defined(CONFIG_FLAT_NODE_MEM_MAP)
+
+/*
+ * Zero all valid struct pages in range [spfn, epfn), return number of struct
+ * pages zeroed
+ */
+static u64 zero_pfn_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;
+ }
+ mm_zero_struct_page(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
@@ -6456,7 +6479,6 @@ void __init free_area_init_node(int nid, unsigned long *zones_size,
void __init zero_resv_unavail(void)
{
phys_addr_t start, end;
- unsigned long pfn;
u64 i, pgcnt;
phys_addr_t next = 0;

@@ -6466,34 +6488,18 @@ void __init zero_resv_unavail(void)
pgcnt = 0;
for_each_mem_range(i, &memblock.memory, NULL,
NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, NULL) {
- if (next < start) {
- for (pfn = PFN_DOWN(next); pfn < PFN_UP(start); pfn++) {
- if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
- continue;
- mm_zero_struct_page(pfn_to_page(pfn));
- pgcnt++;
- }
- }
+ if (next < start)
+ pgcnt += zero_pfn_range(PFN_DOWN(next), PFN_UP(start));
next = end;
}
- for (pfn = PFN_DOWN(next); pfn < max_pfn; pfn++) {
- if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
- continue;
- mm_zero_struct_page(pfn_to_page(pfn));
- pgcnt++;
- }
-
+ pgcnt += zero_pfn_range(PFN_DOWN(next), max_pfn);

/*
* Struct pages that do not have backing memory. This could be because
* firmware is using some of this memory, or for some other reasons.
- * Once memblock is changed so such behaviour is not allowed: i.e.
- * list of "reserved" memory must be a subset of list of "memory", then
- * this code can be removed.
*/
if (pgcnt)
pr_info("Zeroed struct page in unavailable ranges: %lld pages", pgcnt);
-
}
#endif /* CONFIG_HAVE_MEMBLOCK && !CONFIG_FLAT_NODE_MEM_MAP */

--
2.18.0
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