When file refaults are detected and there are many inactive file pages,
the system never reclaim anonymous pages, the file pages are dropped
aggressively when there are still a lot of cold anonymous pages and
system thrashes. This issue impacts the performance of applications
with large executable, e.g. chrome.
Commit 2a2e48854d70 ("mm: vmscan: fix IO/refault regression in cache
workingset transition") introduced actual_reclaim parameter. When file
refaults are detected, inactive_list_is_low() may return different
values depends on the actual_reclaim parameter. Vmscan would only scan
active/inactive file lists at file thrashing state when the following 2
conditions are satisfied.
1) inactive_list_is_low() returns false in get_scan_count() to trigger
scanning file lists only.
2) inactive_list_is_low() returns true in shrink_list() to allow
scanning active file list.
This patch makes the return value of inactive_list_is_low() independent
of actual_reclaim and rename the parameter back to trace.
The problem can be reproduced by the following test program.
---8<---
void fallocate_file(const char *filename, off_t size)
{
struct stat st;
int fd;
if (!stat(filename, &st) && st.st_size >= size)
return;
fd = open(filename, O_WRONLY | O_CREAT, 0600);
if (fd < 0) {
perror("create file");
exit(1);
}
if (posix_fallocate(fd, 0, size)) {
perror("fallocate");
exit(1);
}
close(fd);
}
long *alloc_anon(long size)
{
long *start = malloc(size);
memset(start, 1, size);
return start;
}
long access_file(const char *filename, long size, long rounds)
{
int fd, i;
volatile char *start1, *end1, *start2;
const int page_size = getpagesize();
long sum = 0;
fd = open(filename, O_RDONLY);
if (fd == -1) {
perror("open");
exit(1);
}
/*
* Some applications, e.g. chrome, use a lot of executable file
* pages, map some of the pages with PROT_EXEC flag to simulate
* the behavior.
*/
start1 = mmap(NULL, size / 2, PROT_READ | PROT_EXEC, MAP_SHARED,
fd, 0);
if (start1 == MAP_FAILED) {
perror("mmap");
exit(1);
}
end1 = start1 + size / 2;
start2 = mmap(NULL, size / 2, PROT_READ, MAP_SHARED, fd, size / 2);
if (start2 == MAP_FAILED) {
perror("mmap");
exit(1);
}
for (i = 0; i < rounds; ++i) {
struct timeval before, after;
volatile char *ptr1 = start1, *ptr2 = start2;
gettimeofday(&before, NULL);
for (; ptr1 < end1; ptr1 += page_size, ptr2 += page_size)
sum += *ptr1 + *ptr2;
gettimeofday(&after, NULL);
printf("File access time, round %d: %f (sec)\n", i,
(after.tv_sec - before.tv_sec) +
(after.tv_usec - before.tv_usec) / 1000000.0);
}
return sum;
}
int main(int argc, char *argv[])
{
const long MB = 1024 * 1024;
long anon_mb, file_mb, file_rounds;
const char filename[] = "large";
long *ret1;
long ret2;
if (argc != 4) {
printf("usage: thrash ANON_MB FILE_MB FILE_ROUNDS\n");
exit(0);
}
anon_mb = atoi(argv[1]);
file_mb = atoi(argv[2]);
file_rounds = atoi(argv[3]);
fallocate_file(filename, file_mb * MB);
printf("Allocate %ld MB anonymous pages\n", anon_mb);
ret1 = alloc_anon(anon_mb * MB);
printf("Access %ld MB file pages\n", file_mb);
ret2 = access_file(filename, file_mb * MB, file_rounds);
printf("Print result to prevent optimization: %ld\n",
*ret1 + ret2);
return 0;
}
---8<---
Running the test program on 2GB RAM VM with kernel 5.2.0-rc5, the
program fills ram with 2048 MB memory, access a 200 MB file for 10
times. Without this patch, the file cache is dropped aggresively and
every access to the file is from disk.
$ ./thrash 2048 200 10
Allocate 2048 MB anonymous pages
Access 200 MB file pages
File access time, round 0: 2.489316 (sec)
File access time, round 1: 2.581277 (sec)
File access time, round 2: 2.487624 (sec)
File access time, round 3: 2.449100 (sec)
File access time, round 4: 2.420423 (sec)
File access time, round 5: 2.343411 (sec)
File access time, round 6: 2.454833 (sec)
File access time, round 7: 2.483398 (sec)
File access time, round 8: 2.572701 (sec)
File access time, round 9: 2.493014 (sec)
With this patch, these file pages can be cached.
$ ./thrash 2048 200 10
Allocate 2048 MB anonymous pages
Access 200 MB file pages
File access time, round 0: 2.475189 (sec)
File access time, round 1: 2.440777 (sec)
File access time, round 2: 2.411671 (sec)
File access time, round 3: 1.955267 (sec)
File access time, round 4: 0.029924 (sec)
File access time, round 5: 0.000808 (sec)
File access time, round 6: 0.000771 (sec)
File access time, round 7: 0.000746 (sec)
File access time, round 8: 0.000738 (sec)
File access time, round 9: 0.000747 (sec)
Fixes: 2a2e48854d70 ("mm: vmscan: fix IO/refault regression in cache workingset transition")
Signed-off-by: Kuo-Hsin Yang <vovoy@xxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
mm/vmscan.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7889f583ced9f..da0b97204372e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2125,7 +2125,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
* 10TB 320 32GB
*/
static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
- struct scan_control *sc, bool actual_reclaim)
+ struct scan_control *sc, bool trace)
{
enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE;
struct pglist_data *pgdat = lruvec_pgdat(lruvec);
@@ -2151,7 +2151,7 @@ static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
* rid of the stale workingset quickly.
*/
refaults = lruvec_page_state_local(lruvec, WORKINGSET_ACTIVATE);
- if (file && actual_reclaim && lruvec->refaults != refaults) {
+ if (file && lruvec->refaults != refaults) {
inactive_ratio = 0;
} else {
gb = (inactive + active) >> (30 - PAGE_SHIFT);
@@ -2161,7 +2161,7 @@ static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
inactive_ratio = 1;
}
- if (actual_reclaim)
+ if (trace)
trace_mm_vmscan_inactive_list_is_low(pgdat->node_id, sc->reclaim_idx,
lruvec_lru_size(lruvec, inactive_lru, MAX_NR_ZONES), inactive,
lruvec_lru_size(lruvec, active_lru, MAX_NR_ZONES), active,
--
2.22.0.410.gd8fdbe21b5-goog
