Hi Nhat, On Thu, Dec 7, 2023 at 11:24 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote: > > 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@xxxxxxxxx/ > > as it also disables the zswap shrinker, a major source of zswap > writebacks. I am wondering about the status of "memory.swap.tiers" proof of concept patch? Are we still on board to have this two patch merge together somehow so we can have "memory.swap.tiers" == "all" and "memory.swap.tiers" == "zswap" cover the memory.zswap.writeback == 1 and memory.zswap.writeback == 0 case? Thanks Chris > > Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx> > Reviewed-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > --- > Documentation/admin-guide/cgroup-v2.rst | 12 ++++++++ > Documentation/admin-guide/mm/zswap.rst | 6 ++++ > include/linux/memcontrol.h | 12 ++++++++ > include/linux/zswap.h | 6 ++++ > mm/memcontrol.c | 38 +++++++++++++++++++++++++ > mm/page_io.c | 6 ++++ > mm/shmem.c | 3 +- > mm/zswap.c | 13 +++++++-- > 8 files changed, 92 insertions(+), 4 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 3f85254f3cef..2b4ac43efdc8 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1679,6 +1679,18 @@ PAGE_SIZE multiple when read back. > limit, it will refuse to take any more stores before existing > entries fault back in or are written out to disk. > > + memory.zswap.writeback > + A read-write single value file. The default value is "1". The > + initial value of the root cgroup is 1, and when a new cgroup is > + created, it inherits the current value of its parent. > + > + When this is set to 0, all swapping attempts to swapping devices > + are disabled. This included both zswap writebacks, and swapping due > + to zswap store failure. > + > + Note that this is subtly different from setting memory.swap.max to > + 0, as it still allows for pages to be written to the zswap pool. > + > memory.pressure > A read-only nested-keyed file. > > diff --git a/Documentation/admin-guide/mm/zswap.rst b/Documentation/admin-guide/mm/zswap.rst > index 62fc244ec702..cfa653130346 100644 > --- a/Documentation/admin-guide/mm/zswap.rst > +++ b/Documentation/admin-guide/mm/zswap.rst > @@ -153,6 +153,12 @@ attribute, e. g.:: > > Setting this parameter to 100 will disable the hysteresis. > > +Some users cannot tolerate the swapping that comes with zswap store failures > +and zswap writebacks. Swapping can be disabled entirely (without disabling > +zswap itself) on a cgroup-basis as follows: > + > + echo 0 > /sys/fs/cgroup/<cgroup-name>/memory.zswap.writeback > + > When there is a sizable amount of cold memory residing in the zswap pool, it > can be advantageous to proactively write these cold pages to swap and reclaim > the memory for other use cases. By default, the zswap shrinker is disabled. > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 43b77363ab8e..5de775e6cdd9 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -219,6 +219,12 @@ struct mem_cgroup { > > #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP) > unsigned long zswap_max; > + > + /* > + * Prevent pages from this memcg from being written back from zswap to > + * swap, and from being swapped out on zswap store failures. > + */ > + bool zswap_writeback; > #endif > > unsigned long soft_limit; > @@ -1941,6 +1947,7 @@ static inline void count_objcg_event(struct obj_cgroup *objcg, > bool obj_cgroup_may_zswap(struct obj_cgroup *objcg); > void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size); > void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size); > +bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg); > #else > static inline bool obj_cgroup_may_zswap(struct obj_cgroup *objcg) > { > @@ -1954,6 +1961,11 @@ static inline void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, > size_t size) > { > } > +static inline bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg) > +{ > + /* if zswap is disabled, do not block pages going to the swapping device */ > + return true; > +} > #endif > > #endif /* _LINUX_MEMCONTROL_H */ > diff --git a/include/linux/zswap.h b/include/linux/zswap.h > index 08c240e16a01..a78ceaf3a65e 100644 > --- a/include/linux/zswap.h > +++ b/include/linux/zswap.h > @@ -35,6 +35,7 @@ void zswap_swapoff(int type); > void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg); > void zswap_lruvec_state_init(struct lruvec *lruvec); > void zswap_page_swapin(struct page *page); > +bool is_zswap_enabled(void); > #else > > struct zswap_lruvec_state {}; > @@ -55,6 +56,11 @@ static inline void zswap_swapoff(int type) {} > static inline void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg) {} > static inline void zswap_lruvec_state_init(struct lruvec *lruvec) {} > static inline void zswap_page_swapin(struct page *page) {} > + > +static inline bool is_zswap_enabled(void) > +{ > + return false; > +} > #endif > > #endif /* _LINUX_ZSWAP_H */ > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d7bc47316acb..ae8c62c7aa53 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) { > @@ -8174,6 +8176,12 @@ 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) > { > @@ -8206,6 +8214,31 @@ 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", > @@ -8218,6 +8251,11 @@ 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 */ > diff --git a/mm/page_io.c b/mm/page_io.c > index cb559ae324c6..5e606f1aa2f6 100644 > --- a/mm/page_io.c > +++ b/mm/page_io.c > @@ -201,6 +201,12 @@ int swap_writepage(struct page *page, struct writeback_control *wbc) > folio_end_writeback(folio); > return 0; > } > + > + if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) { > + folio_mark_dirty(folio); > + return AOP_WRITEPAGE_ACTIVATE; > + } > + > __swap_writepage(&folio->page, wbc); > return 0; > } > diff --git a/mm/shmem.c b/mm/shmem.c > index c62f904ba1ca..dd084fbafcf1 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1514,8 +1514,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) > > mutex_unlock(&shmem_swaplist_mutex); > BUG_ON(folio_mapped(folio)); > - swap_writepage(&folio->page, wbc); > - return 0; > + return swap_writepage(&folio->page, wbc); > } > > mutex_unlock(&shmem_swaplist_mutex); > diff --git a/mm/zswap.c b/mm/zswap.c > index daaa949837f2..7ee54a3d8281 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -153,6 +153,11 @@ static bool zswap_shrinker_enabled = IS_ENABLED( > CONFIG_ZSWAP_SHRINKER_DEFAULT_ON); > module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644); > > +bool is_zswap_enabled(void) > +{ > + return zswap_enabled; > +} > + > /********************************* > * data structures > **********************************/ > @@ -596,7 +601,8 @@ static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, > struct zswap_pool *pool = shrinker->private_data; > bool encountered_page_in_swapcache = false; > > - if (!zswap_shrinker_enabled) { > + if (!zswap_shrinker_enabled || > + !mem_cgroup_zswap_writeback_enabled(sc->memcg)) { > sc->nr_scanned = 0; > return SHRINK_STOP; > } > @@ -637,7 +643,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker, > struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid)); > unsigned long nr_backing, nr_stored, nr_freeable, nr_protected; > > - if (!zswap_shrinker_enabled) > + if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(memcg)) > return 0; > > #ifdef CONFIG_MEMCG_KMEM > @@ -956,6 +962,9 @@ static int shrink_memcg(struct mem_cgroup *memcg) > struct zswap_pool *pool; > int nid, shrunk = 0; > > + if (!mem_cgroup_zswap_writeback_enabled(memcg)) > + return -EINVAL; > + > /* > * Skip zombies because their LRUs are reparented and we would be > * reclaiming from the parent instead of the dead memcg. > > base-commit: cdcab2d34f129f593c0afbb2493bcaf41f4acd61 > -- > 2.34.1 >
