mm: incorporate zero pages into transparent huge pages
This patch improves THP collapse rates, by allowing zero pages.
Currently THP can collapse 4kB pages into a THP when there are up to
khugepaged_max_ptes_none pte_none ptes in a 2MB range. This patch counts
pte none and mapped zero pages with the same variable.
The patch was tested with a program that allocates 800MB of
memory, and performs interleaved reads and writes, in a pattern
that causes some 2MB areas to first see read accesses, resulting
in the zero pfn being mapped there.
To simulate memory fragmentation at allocation time, I modified
do_huge_pmd_anonymous_page to return VM_FAULT_FALLBACK for read faults.
Without the patch, only %50 of the program was collapsed into THP and the
percentage did not increase over time.
With this patch after 10 minutes of waiting khugepaged had collapsed %99
of the program's memory.
[aarcange@redhat.com: fix bogus BUG()]
Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 10a4b6c..6352c1d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2109,7 +2109,7 @@
{
while (--_pte >= pte) {
pte_t pteval = *_pte;
- if (!pte_none(pteval))
+ if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
release_pte_page(pte_page(pteval));
}
}
@@ -2120,13 +2120,13 @@
{
struct page *page;
pte_t *_pte;
- int none = 0;
+ int none_or_zero = 0;
bool referenced = false, writable = false;
for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
- if (pte_none(pteval)) {
- if (++none <= khugepaged_max_ptes_none)
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ if (++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
goto out;
@@ -2207,9 +2207,21 @@
pte_t pteval = *_pte;
struct page *src_page;
- if (pte_none(pteval)) {
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
clear_user_highpage(page, address);
add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
+ if (is_zero_pfn(pte_pfn(pteval))) {
+ /*
+ * ptl mostly unnecessary.
+ */
+ spin_lock(ptl);
+ /*
+ * paravirt calls inside pte_clear here are
+ * superfluous.
+ */
+ pte_clear(vma->vm_mm, address, _pte);
+ spin_unlock(ptl);
+ }
} else {
src_page = pte_page(pteval);
copy_user_highpage(page, src_page, address, vma);
@@ -2543,7 +2555,7 @@
{
pmd_t *pmd;
pte_t *pte, *_pte;
- int ret = 0, none = 0;
+ int ret = 0, none_or_zero = 0;
struct page *page;
unsigned long _address;
spinlock_t *ptl;
@@ -2561,8 +2573,8 @@
for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
_pte++, _address += PAGE_SIZE) {
pte_t pteval = *_pte;
- if (pte_none(pteval)) {
- if (++none <= khugepaged_max_ptes_none)
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
+ if (++none_or_zero <= khugepaged_max_ptes_none)
continue;
else
goto out_unmap;