The patch titled
Subject: x86/vmemmap: handle unpopulated sub-pmd ranges
has been added to the -mm tree. Its filename is
x86-vmemmap-handle-unpopulated-sub-pmd-ranges.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/x86-vmemmap-handle-unpopulated-sub-pmd-ranges.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/x86-vmemmap-handle-unpopulated-sub-pmd-ranges.patch
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------------------------------------------------------
From: Oscar Salvador <osalvador@xxxxxxx>
Subject: x86/vmemmap: handle unpopulated sub-pmd ranges
When the size of a struct page is not multiple of 2MB, sections do not
span a PMD anymore and so when populating them some parts of the PMD will
remain unused. Because of this, PMDs will be left behind when
depopulating sections since remove_pmd_table() thinks that those unused
parts are still in use.
Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv()
will do the right thing and will let us free the PMD when the last user of
it is gone.
This patch is based on a similar patch by David Hildenbrand:
https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@xxxxxxxxxx/
https://lore.kernel.org/linux-mm/20200722094558.9828-10-david@xxxxxxxxxx/
Link: https://lkml.kernel.org/r/20210301083230.30924-4-osalvador@xxxxxxx
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/init_64.c | 106 ++++++++++++++++++++++++++++++++++++----
1 file changed, 98 insertions(+), 8 deletions(-)
--- a/arch/x86/mm/init_64.c~x86-vmemmap-handle-unpopulated-sub-pmd-ranges
+++ a/arch/x86/mm/init_64.c
@@ -871,7 +871,93 @@ int arch_add_memory(int nid, u64 start,
return add_pages(nid, start_pfn, nr_pages, params);
}
-#define PAGE_INUSE 0xFD
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+#define PAGE_UNUSED 0xFD
+
+/*
+ * The unused vmemmap range, which was not yet memset(PAGE_UNUSED) ranges
+ * from unused_pmd_start to next PMD_SIZE boundary.
+ */
+static unsigned long unused_pmd_start __meminitdata;
+
+static void __meminit vmemmap_flush_unused_pmd(void)
+{
+ if (!unused_pmd_start)
+ return;
+ /*
+ * Clears (unused_pmd_start, PMD_END]
+ */
+ memset((void *)unused_pmd_start, PAGE_UNUSED,
+ ALIGN(unused_pmd_start, PMD_SIZE) - unused_pmd_start);
+ unused_pmd_start = 0;
+}
+
+/* Returns true if the PMD is completely unused and thus it can be freed */
+static bool __meminit vmemmap_unuse_sub_pmd(unsigned long addr, unsigned long end)
+{
+ unsigned long start = ALIGN_DOWN(addr, PMD_SIZE);
+
+ vmemmap_flush_unused_pmd();
+ memset((void *)addr, PAGE_UNUSED, end - addr);
+
+ return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE);
+}
+
+static void __meminit __vmemmap_use_sub_pmd(unsigned long start)
+{
+ /*
+ * As we expect to add in the same granularity as we remove, it's
+ * sufficient to mark only some piece used to block the memmap page from
+ * getting removed when removing some other adjacent memmap (just in
+ * case the first memmap never gets initialized e.g., because the memory
+ * block never gets onlined).
+ */
+ memset((void *)start, 0, sizeof(struct page));
+}
+
+static void __meminit vmemmap_use_sub_pmd(unsigned long start, unsigned long end)
+{
+ /*
+ * We only optimize if the new used range directly follows the
+ * previously unused range (esp., when populating consecutive sections).
+ */
+ if (unused_pmd_start == start) {
+ if (likely(IS_ALIGNED(end, PMD_SIZE)))
+ unused_pmd_start = 0;
+ else
+ unused_pmd_start = end;
+ return;
+ }
+
+ vmemmap_flush_unused_pmd();
+ __vmemmap_use_sub_pmd(start);
+}
+
+static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end)
+{
+ vmemmap_flush_unused_pmd();
+
+ /*
+ * Could be our memmap page is filled with PAGE_UNUSED already from a
+ * previous remove.
+ */
+ __vmemmap_use_sub_pmd(start);
+
+ /*
+ * Mark the unused parts of the new memmap range
+ */
+ if (!IS_ALIGNED(start, PMD_SIZE))
+ memset((void *)start, PAGE_UNUSED,
+ start - ALIGN_DOWN(start, PMD_SIZE));
+ /*
+ * We want to avoid memset(PAGE_UNUSED) when populating the vmemmap of
+ * consecutive sections. Remember for the last added PMD the last
+ * unused range in the populated PMD.
+ */
+ if (!IS_ALIGNED(end, PMD_SIZE))
+ unused_pmd_start = end;
+}
+#endif
static void __meminit free_pagetable(struct page *page, int order)
{
@@ -1006,7 +1092,6 @@ remove_pmd_table(pmd_t *pmd_start, unsig
unsigned long next, pages = 0;
pte_t *pte_base;
pmd_t *pmd;
- void *page_addr;
pmd = pmd_start + pmd_index(addr);
for (; addr < end; addr = next, pmd++) {
@@ -1027,12 +1112,11 @@ remove_pmd_table(pmd_t *pmd_start, unsig
spin_unlock(&init_mm.page_table_lock);
pages++;
} else {
- /* If here, we are freeing vmemmap pages. */
- memset((void *)addr, PAGE_INUSE, next - addr);
-
- page_addr = page_address(pmd_page(*pmd));
- if (!memchr_inv(page_addr, PAGE_INUSE,
- PMD_SIZE)) {
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+ /*
+ * Free the PMD if the whole range is unused.
+ */
+ if (vmemmap_unuse_sub_pmd(addr, next)) {
free_hugepage_table(pmd_page(*pmd),
altmap);
@@ -1040,6 +1124,7 @@ remove_pmd_table(pmd_t *pmd_start, unsig
pmd_clear(pmd);
spin_unlock(&init_mm.page_table_lock);
}
+#endif
}
continue;
@@ -1492,11 +1577,16 @@ static int __meminit vmemmap_populate_hu
addr_end = addr + PMD_SIZE;
p_end = p + PMD_SIZE;
+
+ if (!IS_ALIGNED(addr, PMD_SIZE) ||
+ !IS_ALIGNED(next, PMD_SIZE))
+ vmemmap_use_new_sub_pmd(addr, next);
continue;
} else if (altmap)
return -ENOMEM; /* no fallback */
} else if (pmd_large(*pmd)) {
vmemmap_verify((pte_t *)pmd, node, addr, next);
+ vmemmap_use_sub_pmd(addr, next);
continue;
}
if (vmemmap_populate_basepages(addr, next, node, NULL))
_
Patches currently in -mm which might be from osalvador@xxxxxxx are
x86-vmemmap-drop-handling-of-4k-unaligned-vmemmap-range.patch
x86-vmemmap-drop-handling-of-1gb-vmemmap-ranges.patch
x86-vmemmap-handle-unpopulated-sub-pmd-ranges.patch
