[Devel] [PATCH VZ10 1/4] ve/proc: Fix meminfo swap calculations on cgroup-v2

[Pavel Tikhomirov]

The memsw counter in cgroup-v2 is reused by swap counter and does not
include memory usage, we should use it directly instead of subtracting
memory from memsw.

While on it let's reorder loading memused, memtotal, swapused and
swaptotal before doing any calculations or corrections on them, and also
fix comment style.

https://virtuozzo.atlassian.net/browse/VSTOR-105819
Fixes: 6992eead25249 ("ve/proc: virtualize /proc/meminfo in a Container")
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

Feature: procfs: virtualize /proc/meminfo
---
 mm/show_mem.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/mm/show_mem.c b/mm/show_mem.c
index be4985e672dc4..0453e3c635eb2 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -106,13 +106,23 @@ void si_meminfo_ve(struct sysinfo *si, struct ve_struct *ve)
 
 	memtotal = READ_ONCE(memcg->memory.max);
 	memused = page_counter_read(&memcg->memory);
-	si->totalram = memtotal;
 
-	swaptotal = READ_ONCE(memcg->memsw.max) - memtotal;
-	swapused = page_counter_read(&memcg->memsw) - memused;
+	if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
+		swaptotal = READ_ONCE(memcg->swap.max);
+		swapused = page_counter_read(&memcg->swap);
+	} else {
+		swaptotal = READ_ONCE(memcg->memsw.max) - memtotal;
+		swapused = page_counter_read(&memcg->memsw) - memused;
+	}
+
+	si->totalram = memtotal;
 	si->totalswap = swaptotal;
-	/* Due to global reclaim, memory.memsw.usage can be greater than
-	 * (memory.memsw.max - memory.max). */
+
+	/*
+	 * Due to global reclaim, memory.memsw.usage can be greater than
+	 * (memory.memsw.max - memory.max), and we show this "excess" swap
+	 * usage as if it's memory usage.
+	 */
 	if (swaptotal >= swapused) {
 		si->freeswap = swaptotal - swapused;
 	} else {
-- 
2.51.0