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.
With this patch, when file refault is detected, inactive_list_is_low() always returns true for file pages in get_scan_count() to enable scanning anonymous pages.
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: e9868505987a ("mm,vmscan: only evict file pages when we have plenty") Fixes: 7c5bd705d8f9 ("mm: memcg: only evict file pages when we have plenty") Signed-off-by: Kuo-Hsin Yang vovoy@chromium.org Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: stable@vger.kernel.org # 4.12+ --- 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,