The patch titled
Subject: mm: add defines for min/max swappiness
has been added to the -mm mm-unstable branch. Its filename is
mm-add-defines-for-min-max-swappiness.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-defines-for-min-max-swappiness.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
Subject: mm: add defines for min/max swappiness
Date: Wed, 3 Jan 2024 08:48:36 -0800
Patch series "Add swappiness argument to memory.reclaim", v6.
This patch proposes augmenting the memory.reclaim interface with a
swappiness=<val> argument that overrides the swappiness value for that
instance of proactive reclaim.
Userspace proactive reclaimers use the memory.reclaim interface to trigger
reclaim. The memory.reclaim interface does not allow for any way to
effect the balance of file vs anon during proactive reclaim. The only
approach is to adjust the vm.swappiness setting. However, there are a few
reasons we look to control the balance of file vs anon during proactive
reclaim, separately from reactive reclaim:
* Swapout should be limited to manage SSD write endurance. In near-OOM
situations we are fine with lots of swap-out to avoid OOMs. As these
are typically rare events, they have relatively little impact on write
endurance. However, proactive reclaim runs continuously and so its
impact on SSD write endurance is more significant. Therefore it is
desireable to control swap-out for proactive reclaim separately from
reactive reclaim
* Some userspace OOM killers like systemd-oomd[1] support OOM killing on
swap exhaustion. This makes sense if the swap exhaustion is triggered
due to reactive reclaim but less so if it is triggered due to proactive
reclaim (e.g. one could see OOMs when free memory is ample but anon is
just particularly cold). Therefore, it's desireable to have proactive
reclaim reduce or stop swap-out before the threshold at which OOM
killing occurs.
In the case of Meta's Senpai proactive reclaimer, we adjust vm.swappiness
before writes to memory.reclaim[2]. This has been in production for
nearly two years and has addressed our needs to control proactive vs
reactive reclaim behavior but is still not ideal for a number of reasons:
* vm.swappiness is a global setting, adjusting it can race/interfere
with other system administration that wishes to control vm.swappiness.
In our case, we need to disable Senpai before adjusting vm.swappiness.
* vm.swappiness is stateful - so a crash or restart of Senpai can leave
a misconfigured setting. This requires some additional management to
record the "desired" setting and ensure Senpai always adjusts to it.
With this patch, we avoid these downsides of adjusting vm.swappiness
globally.
Previously, this exact interface addition was proposed by Yosry[3]. In
response, Roman proposed instead an interface to specify precise
file/anon/slab reclaim amounts[4]. More recently Huan also proposed this
as well[5] and others similarly questioned if this was the proper
interface.
Previous proposals sought to use this to allow proactive reclaimers to
effectively perform a custom reclaim algorithm by issuing proactive
reclaim with different settings to control file vs anon reclaim (e.g. to
only reclaim anon from some applications). Responses argued that
adjusting swappiness is a poor interface for custom reclaim.
In contrast, I argue in favor of a swappiness setting not as a way to
implement custom reclaim algorithms but rather to bias the balance of anon
vs file due to differences of proactive vs reactive reclaim. In this
context, swappiness is the existing interface for controlling this balance
and this patch simply allows for it to be configured differently for
proactive vs reactive reclaim.
Specifying explicit amounts of anon vs file pages to reclaim feels
inappropriate for this prupose. Proactive reclaimers are un-aware of the
relative age of file vs anon for a cgroup which makes it difficult to
manage proactive reclaim of different memory pools. A proactive reclaimer
would need some amount of anon reclaim attempts separate from the amount
of file reclaim attempts which seems brittle given that it's difficult to
observe the impact.
[1]https://www.freedesktop.org/software/systemd/man/latest/systemd-oomd.service.html
[2]https://github.com/facebookincubator/oomd/blob/main/src/oomd/plugins/Senpai.cpp#L585-L598
[3]https://lore.kernel.org/linux-mm/CAJD7tkbDpyoODveCsnaqBBMZEkDvshXJmNdbk51yKSNgD7aGdg@xxxxxxxxxxxxxx/
[4]https://lore.kernel.org/linux-mm/YoPHtHXzpK51F%2F1Z@carbon/
[5]https://lore.kernel.org/lkml/20231108065818.19932-1-link@xxxxxxxx/
This patch (of 2):
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.
Link: https://lkml.kernel.org/r/20240103164841.2800183-1-schatzberg.dan@xxxxxxxxx
Link: https://lkml.kernel.org/r/20240103164841.2800183-2-schatzberg.dan@xxxxxxxxx
Signed-off-by: Dan Schatzberg <schatzberg.dan@xxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: Chris Li <chrisl@xxxxxxxxxx>
Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Yue Zhao <findns94@xxxxxxxxx>
Cc: Zefan Li <lizefan.x@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/swap.h | 2 ++
mm/memcontrol.c | 2 +-
mm/vmscan.c | 14 +++++++-------
3 files changed, 10 insertions(+), 8 deletions(-)
--- a/include/linux/swap.h~mm-add-defines-for-min-max-swappiness
+++ a/include/linux/swap.h
@@ -404,6 +404,8 @@ extern unsigned long try_to_free_pages(s
#define MEMCG_RECLAIM_MAY_SWAP (1 << 1)
#define MEMCG_RECLAIM_PROACTIVE (1 << 2)
+#define MIN_SWAPPINESS 0
+#define MAX_SWAPPINESS 200
extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
unsigned long nr_pages,
gfp_t gfp_mask,
--- a/mm/memcontrol.c~mm-add-defines-for-min-max-swappiness
+++ a/mm/memcontrol.c
@@ -4356,7 +4356,7 @@ static int mem_cgroup_swappiness_write(s
{
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
- if (val > 200)
+ if (val > MAX_SWAPPINESS)
return -EINVAL;
if (!mem_cgroup_is_root(memcg))
--- a/mm/vmscan.c~mm-add-defines-for-min-max-swappiness
+++ a/mm/vmscan.c
@@ -183,7 +183,7 @@ struct scan_control {
#endif
/*
- * From 0 .. 200. Higher means more swappy.
+ * From 0 .. MAX_SWAPPINESS. Higher means more swappy.
*/
int vm_swappiness = 60;
@@ -2404,7 +2404,7 @@ static void get_scan_count(struct lruvec
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;
@@ -4422,7 +4422,7 @@ static int get_type_to_scan(struct lruve
{
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
@@ -4458,7 +4458,7 @@ static int isolate_folios(struct lruvec
/*
* Try to make the obvious choice first. When anon and file are both
* available from the same generation, interpret swappiness 1 as file
- * first and 200 as anon first.
+ * first and MAX_SWAPPINESS as anon first.
*/
if (!swappiness)
type = LRU_GEN_FILE;
@@ -4466,7 +4466,7 @@ static int isolate_folios(struct lruvec
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);
@@ -5408,9 +5408,9 @@ static int run_cmd(char cmd, int memcg_i
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) {
_
Patches currently in -mm which might be from schatzberg.dan@xxxxxxxxx are
mm-add-defines-for-min-max-swappiness.patch
mm-add-swapiness=-arg-to-memoryreclaim.patch
