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authorNhat Pham <nphamcs@gmail.com>2023-12-07 11:24:06 -0800
committerAndrew Morton <akpm@linux-foundation.org>2023-12-29 20:22:11 -0800
commit501a06fe8e4c185bbda371b8cedbdf1b23a633d8 (patch)
tree4aefe7c3ca0b38f8f0e99dc11f38c83d7b66cc1b /mm/memcontrol.c
parent1ae41dffd48a700f4bf69e5377f4311de7d92b78 (diff)
zswap: memcontrol: implement zswap writeback disabling
During our experiment with zswap, we sometimes observe swap IOs due to occasional zswap store failures and writebacks-to-swap. These swapping IOs prevent many users who cannot tolerate swapping from adopting zswap to save memory and improve performance where possible. This patch adds the option to disable this behavior entirely: do not writeback to backing swapping device when a zswap store attempt fail, and do not write pages in the zswap pool back to the backing swap device (both when the pool is full, and when the new zswap shrinker is called). This new behavior can be opted-in/out on a per-cgroup basis via a new cgroup file. By default, writebacks to swap device is enabled, which is the previous behavior. Initially, writeback is enabled for the root cgroup, and a newly created cgroup will inherit the current setting of its parent. Note that this is subtly different from setting memory.swap.max to 0, as it still allows for pages to be stored in the zswap pool (which itself consumes swap space in its current form). This patch should be applied on top of the zswap shrinker series: https://lore.kernel.org/linux-mm/20231130194023.4102148-1-nphamcs@gmail.com/ as it also disables the zswap shrinker, a major source of zswap writebacks. For the most part, this feature is motivated by internal parties who have already established their opinions regarding swapping - the workloads that are highly sensitive to IO, and especially those who are using servers with really slow disk performance (for instance, massive but slow HDDs). For these folks, it's impossible to convince them to even entertain zswap if swapping also comes as a packaged deal. Writeback disabling is quite a useful feature in these situations - on a mixed workloads deployment, they can disable writeback for the more IO-sensitive workloads, and enable writeback for other background workloads. For instance, on a server with HDD, I allocate memories and populate them with random values (so that zswap store will always fail), and specify memory.high low enough to trigger reclaim. The time it takes to allocate the memories and just read through it a couple of times (doing silly things like computing the values' average etc.): zswap.writeback disabled: real 0m30.537s user 0m23.687s sys 0m6.637s 0 pages swapped in 0 pages swapped out zswap.writeback enabled: real 0m45.061s user 0m24.310s sys 0m8.892s 712686 pages swapped in 461093 pages swapped out (the last two lines are from vmstat -s). [nphamcs@gmail.com: add a comment about recurring zswap store failures leading to reclaim inefficiency] Link: https://lkml.kernel.org/r/20231221005725.3446672-1-nphamcs@gmail.com Link: https://lkml.kernel.org/r/20231207192406.3809579-1-nphamcs@gmail.com Signed-off-by: Nhat Pham <nphamcs@gmail.com> Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Yosry Ahmed <yosryahmed@google.com> Acked-by: Chris Li <chrisl@kernel.org> Cc: Dan Streetman <ddstreet@ieee.org> Cc: David Heidelberg <david@ixit.cz> Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Seth Jennings <sjenning@redhat.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Tejun Heo <tj@kernel.org> Cc: Vitaly Wool <vitaly.wool@konsulko.com> Cc: Zefan Li <lizefan.x@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r--mm/memcontrol.c38
1 files changed, 38 insertions, 0 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b08b9cd4a3a8..3ca691fb5b49 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5538,6 +5538,8 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
WRITE_ONCE(memcg->soft_limit, PAGE_COUNTER_MAX);
#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
memcg->zswap_max = PAGE_COUNTER_MAX;
+ WRITE_ONCE(memcg->zswap_writeback,
+ !parent || READ_ONCE(parent->zswap_writeback));
#endif
page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX);
if (parent) {
@@ -8166,6 +8168,12 @@ void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size)
rcu_read_unlock();
}
+bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
+{
+ /* if zswap is disabled, do not block pages going to the swapping device */
+ return !is_zswap_enabled() || !memcg || READ_ONCE(memcg->zswap_writeback);
+}
+
static u64 zswap_current_read(struct cgroup_subsys_state *css,
struct cftype *cft)
{
@@ -8198,6 +8206,31 @@ static ssize_t zswap_max_write(struct kernfs_open_file *of,
return nbytes;
}
+static int zswap_writeback_show(struct seq_file *m, void *v)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
+
+ seq_printf(m, "%d\n", READ_ONCE(memcg->zswap_writeback));
+ return 0;
+}
+
+static ssize_t zswap_writeback_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+ int zswap_writeback;
+ ssize_t parse_ret = kstrtoint(strstrip(buf), 0, &zswap_writeback);
+
+ if (parse_ret)
+ return parse_ret;
+
+ if (zswap_writeback != 0 && zswap_writeback != 1)
+ return -EINVAL;
+
+ WRITE_ONCE(memcg->zswap_writeback, zswap_writeback);
+ return nbytes;
+}
+
static struct cftype zswap_files[] = {
{
.name = "zswap.current",
@@ -8210,6 +8243,11 @@ static struct cftype zswap_files[] = {
.seq_show = zswap_max_show,
.write = zswap_max_write,
},
+ {
+ .name = "zswap.writeback",
+ .seq_show = zswap_writeback_show,
+ .write = zswap_writeback_write,
+ },
{ } /* terminate */
};
#endif /* CONFIG_MEMCG_KMEM && CONFIG_ZSWAP */