On Thu, Dec 03, 2020 at 10:53:33AM +0800, Muchun Song wrote:

On Thu, Dec 3, 2020 at 5:16 AM Roman Gushchin [off-list ref] wrote:

quoted

On Wed, Dec 02, 2020 at 08:14:34PM +0800, Muchun Song wrote:

quoted

Although the ratio of the slab is one, we also should read the ratio
from the related memory_stats instead of hard-coding. And the local
variable of size is already the value of slab_unreclaimable. So we
do not need to read again. Simplify the code here.

Signed-off-by: Muchun Song <redacted>
---
 mm/memcontrol.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

Hi Muchun!

quoted

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9922f1510956..03a9c64560f6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -1545,12 +1545,22 @@ static int __init memory_stats_init(void)
      int i;

      for (i = 0; i < ARRAY_SIZE(memory_stats); i++) {
+             switch (memory_stats[i].idx) {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-             if (memory_stats[i].idx == NR_ANON_THPS ||
-                 memory_stats[i].idx == NR_FILE_THPS ||
-                 memory_stats[i].idx == NR_SHMEM_THPS)
+             case NR_ANON_THPS:
+             case NR_FILE_THPS:
+             case NR_SHMEM_THPS:
                      memory_stats[i].ratio = HPAGE_PMD_SIZE;
+                     break;
 #endif
+             case NR_SLAB_UNRECLAIMABLE_B:
+                     VM_BUG_ON(i < 1);
+                     VM_BUG_ON(memory_stats[i - 1].idx != NR_SLAB_RECLAIMABLE_B);

Please, convert these to BUILD_BUG_ON(), they don't have to be runtime checks.

Agree. But here we cannot use BUILD_BUG_ON(). The compiler will
complain about it.

We can!

We just need to change the condition. All we really need to check is that
NR_SLAB_UNRECLAIMABLE_B immediately following NR_SLAB_RECLAIMABLE_B.

Something like BUILD_BUG_ON(NR_SLAB_UNRECLAIMABLE_B != NR_SLAB_RECLAIMABLE_B + 1)
should work (completely untested).

quoted

quoted

+                     break;
+             default:
+                     break;
+             }
+
              VM_BUG_ON(!memory_stats[i].ratio);
              VM_BUG_ON(memory_stats[i].idx >= MEMCG_NR_STAT);
      }

@@ -1587,8 +1597,10 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
              seq_buf_printf(&s, "%s %llu\n", memory_stats[i].name, size);

Can you, please, add a small comment here stating that we're printing
unreclaimable, reclaimable and the sum of both? It will simplify the reading of the code.

Will do.

Thank you!