In current implementation, process's read requestions will fault in pages
with WP flags in PTEs. Next, if process emit a write requestion will go
into do_wp_page() and copy data to a new allocated page from the old one
due to refcount > 1 (page table mapped and swapcache), which could be
result in performance degradation. In fact, this page is exclusively owned
by this process and the duplication from old to a new allocated page is
really unnecessary.
So In this situation, these unshared pages can be reused by its process.
Signed-off-by: Liang Zhang <zhangliang5@xxxxxxxxxx>
---
This patch has been tested with redis benchmark. Here is the test
result.
Hardware
========
Memory (GB): 512G
CPU (total #): 88
NVMe SSD (GB): 1024
OS
==
kernel 5.10.0
Testcase
========
step 1:
Run 16 VMs (4U8G), each running with redis-server, in a cgroup
limiting memory.limit_in_bytes to 100G.
step 2:
Run memtier_bemchmark in host with params "--threads=1 --clients=1 \
--pipeline=256 --data-size=2048 --requests=allkeys --key-minimum=1 \
--key-maximum=30000000 --key-prefix=memtier-benchmark-prefix-redistests"
to test every VM concurrently.
Workset size
============
cat memory.memsw.usage_in_bytes
125403303936
Result
======
Comparing with Baseline, this patch can achieved 41% more Ops/sec,
41% more Hits/sec, 41% more Misses/sec, 30% less Latency and
41% more KB/sec.
Index(average) Baseline kernel Patched kernel
Ops/sec 109497 155428
Hits/sec 8653 12283
Misses/sec 90889 129014
Latency 2.297 1.603
KB/sec 44569 63186
mm/memory.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 23f2f1300d42..fd4d868b1c2d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3291,10 +3291,16 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
struct page *page = vmf->page;
/* PageKsm() doesn't necessarily raise the page refcount */
- if (PageKsm(page) || page_count(page) != 1)
+ if (PageKsm(page))
goto copy;
if (!trylock_page(page))
goto copy;
+
+ /* reuse the unshared swapcache page */
+ if (PageSwapCache(page) && reuse_swap_page(page, NULL)) {
+ goto reuse;
+ }
+
if (PageKsm(page) || page_mapcount(page) != 1 || page_count(page) != 1) {
unlock_page(page);
goto copy;
@@ -3304,6 +3310,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
* page count reference, and the page is locked,
* it's dark out, and we're wearing sunglasses. Hit it.
*/
+reuse:
unlock_page(page);
wp_page_reuse(vmf);
return VM_FAULT_WRITE;
--
2.30.0
