Re: [PATCH V4 1/2] mm: add defines for min/max swappiness

From: Huan Yang
Date: Tue Dec 12 2023 - 20:58:48 EST



在 2023/12/13 9:38, Dan Schatzberg 写道:
[????????? schatzberg.dan@xxxxxxxxx ????????? https://aka.ms/LearnAboutSenderIdentification,????????????]

We use the constants 0 and 200 in a few places in the mm code when
referring to the min and max swappiness. This patch adds MIN_SWAPPINESS
and MAX_SWAPPINESS #defines to improve clarity. There are no functional
changes.

Signed-off-by: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
---
include/linux/swap.h | 2 ++
mm/memcontrol.c | 2 +-
mm/vmscan.c | 10 +++++-----
3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index f6dd6575b905..e2ab76c25b4a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -407,6 +407,8 @@ extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,

#define MEMCG_RECLAIM_MAY_SWAP (1 << 1)
#define MEMCG_RECLAIM_PROACTIVE (1 << 2)
+#define MIN_SWAPPINESS 0
+#define MAX_SWAPPINESS 200

Do MAX_SWAPPINESS apply for all swapppiness? If so, maybe better change swappiness sysctl define:
```
sysctl.c:

{
        .procname    = "swappiness",
        .data        = &vm_swappiness,
        .maxlen        = sizeof(vm_swappiness),
        .mode        = 0644,
        .proc_handler    = proc_dointvec_minmax,
        .extra1        = SYSCTL_ZERO,
        .extra2        = SYSCTL_TWO_HUNDRED,
    },

```

Here hard code swappiness in [0, 200], and now add a new define.

And many other code hard reference 200 into max value of swappiness, like:

```
memcontrol.c:
static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
                       struct cftype *cft, u64 val)
{
    struct mem_cgroup *memcg = mem_cgroup_from_css(css);

    if (val > 200)
        return -EINVAL;

    if (!mem_cgroup_is_root(memcg))
        memcg->swappiness = val;
    else
        vm_swappiness = val;

    return 0;
}
vmscan.c:

/*
 * From 0 .. 200.  Higher means more swappy.
 */
int vm_swappiness = 60;

```


extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
unsigned long nr_pages,
gfp_t gfp_mask,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1c1061df9cd1..9748a6b88bb8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4337,7 +4337,7 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);

- if (val > 200)
+ if (val > MAX_SWAPPINESS)
return -EINVAL;

if (!mem_cgroup_is_root(memcg))
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 506f8220c5fe..2aa671fe938b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2403,7 +2403,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
ap = swappiness * (total_cost + 1);
ap /= anon_cost + 1;

- fp = (200 - swappiness) * (total_cost + 1);
+ fp = (MAX_SWAPPINESS - swappiness) * (total_cost + 1);
fp /= file_cost + 1;

fraction[0] = ap;
@@ -4400,7 +4400,7 @@ static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_idx
{
int type, tier;
struct ctrl_pos sp, pv;
- int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness };
+ int gain[ANON_AND_FILE] = { swappiness, MAX_SWAPPINESS - swappiness };

/*
* Compare the first tier of anon with that of file to determine which
@@ -4444,7 +4444,7 @@ static int isolate_folios(struct lruvec *lruvec, struct scan_control *sc, int sw
type = LRU_GEN_ANON;
else if (swappiness == 1)
type = LRU_GEN_FILE;
- else if (swappiness == 200)
+ else if (swappiness == MAX_SWAPPINESS)
type = LRU_GEN_ANON;
else
type = get_type_to_scan(lruvec, swappiness, &tier);
@@ -5368,9 +5368,9 @@ static int run_cmd(char cmd, int memcg_id, int nid, unsigned long seq,

lruvec = get_lruvec(memcg, nid);

- if (swappiness < 0)
+ if (swappiness < MIN_SWAPPINESS)
swappiness = get_swappiness(lruvec, sc);
- else if (swappiness > 200)
+ else if (swappiness > MAX_SWAPPINESS)
goto done;

switch (cmd) {
--
2.34.1