| Message ID | 20231102234236.1784543-1-nphamcs@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC,v3] zswap: memcontrol: implement zswap writeback disabling | expand |
On Thu, Nov 2, 2023 at 4:42 PM Nhat Pham <nphamcs@gmail.com> 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. > > 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). > > Suggested-by: Johannes Weiner <hannes@cmpxchg.org> > Signed-off-by: Nhat Pham <nphamcs@gmail.com> > --- > Documentation/admin-guide/cgroup-v2.rst | 11 +++++++ > 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 | 14 +++++++++ > 8 files changed, 94 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index 606b2e0eac4b..18c4171392ea 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1672,6 +1672,17 @@ 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 which exists on non-root > + cgroups. The default value is "1". > + > + 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 522ae22ccb84..b987e58edb70 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 95f6c9e60ed1..e51eafdf2a15 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; > @@ -1931,6 +1937,7 @@ 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) > { > @@ -1944,6 +1951,11 @@ 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 cbd373ba88d2..b4997e27a74b 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_lruvec_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_init(struct lruvec *lruvec) {} > static inline void zswap_lruvec_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 e43b5aba8efc..8a6aadcc103c 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5545,6 +5545,7 @@ 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, true); Generally LGTM, just one question. Would it be more convenient if the initial value is inherited from the parent (the root starts with true)? I can see this being useful if we want to set it to false on the entire machine or one a parent cgroup, we can set it before creating any children instead of setting it to 0 every time we create a new cgroup.
On Thu, Nov 2, 2023 at 6:13 PM Yosry Ahmed <yosryahmed@google.com> wrote: > > On Thu, Nov 2, 2023 at 4:42 PM Nhat Pham <nphamcs@gmail.com> 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. > > > > 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). > > > > Suggested-by: Johannes Weiner <hannes@cmpxchg.org> > > Signed-off-by: Nhat Pham <nphamcs@gmail.com> > > --- > > Documentation/admin-guide/cgroup-v2.rst | 11 +++++++ > > 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 | 14 +++++++++ > > 8 files changed, 94 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > > index 606b2e0eac4b..18c4171392ea 100644 > > --- a/Documentation/admin-guide/cgroup-v2.rst > > +++ b/Documentation/admin-guide/cgroup-v2.rst > > @@ -1672,6 +1672,17 @@ 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 which exists on non-root > > + cgroups. The default value is "1". > > + > > + 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 522ae22ccb84..b987e58edb70 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 95f6c9e60ed1..e51eafdf2a15 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; > > @@ -1931,6 +1937,7 @@ 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) > > { > > @@ -1944,6 +1951,11 @@ 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 cbd373ba88d2..b4997e27a74b 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_lruvec_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_init(struct lruvec *lruvec) {} > > static inline void zswap_lruvec_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 e43b5aba8efc..8a6aadcc103c 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -5545,6 +5545,7 @@ 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, true); > > Generally LGTM, just one question. > > Would it be more convenient if the initial value is inherited from the > parent (the root starts with true)? > > I can see this being useful if we want to set it to false on the > entire machine or one a parent cgroup, we can set it before creating > any children instead of setting it to 0 every time we create a new > cgroup. I'm not 100% sure about the benefit or have a strong opinion one way or another, but this sounds like a nice-to-have detail to me, and a relatively low cost one (both in effort and at runtime) at that too. Propagating the change everytime we modify the memory.zswap.writeback value of the ancestor might be data race-prone (and costly, depending on how big the cgroup subtree is), but this is just a one-time-per-cgroup propagation (at the new cgroup creation time). Can anyone come up with a failure case for this change, or why it might be a bad idea? Thanks for the suggestion, Yosry!
Hi Nhant, On Fri, Nov 3, 2023 at 12:24 PM Nhat Pham <nphamcs@gmail.com> wrote: > > > > Would it be more convenient if the initial value is inherited from the > > parent (the root starts with true)? > > > > I can see this being useful if we want to set it to false on the > > entire machine or one a parent cgroup, we can set it before creating > > any children instead of setting it to 0 every time we create a new > > cgroup. > > I'm not 100% sure about the benefit or have a strong opinion one way > or another, but this sounds like a nice-to-have detail to me, and a relatively > low cost one (both in effort and at runtime) at that too. > > Propagating the change everytime we modify the memory.zswap.writeback > value of the ancestor might be data race-prone (and costly, depending on > how big the cgroup subtree is), but this is just a one-time-per-cgroup > propagation (at the new cgroup creation time). I think Yosary was suggesting inheriting the initial value from parents. That is just one level look up when you create the new cgroup, using the parent value as default. No recursive. What you described above seems different to me. I understand what you are suggesting is that writing to the parent cgroup will recursively write to all child cgroup. > > Can anyone come up with a failure case for this change, or why it might be > a bad idea? I would suggest against recursive changing value behavior. What if you want the parent but also want the child to keep its value not changed? Every change to the parent will have to go through the child to flip it back. Inherit from the parent seems fine. Chris
On Wed, Nov 8, 2023 at 6:41 PM Chris Li <chrisl@kernel.org> wrote: > > Hi Nhant, > > On Fri, Nov 3, 2023 at 12:24 PM Nhat Pham <nphamcs@gmail.com> wrote: > > > > > > Would it be more convenient if the initial value is inherited from the > > > parent (the root starts with true)? > > > > > > I can see this being useful if we want to set it to false on the > > > entire machine or one a parent cgroup, we can set it before creating > > > any children instead of setting it to 0 every time we create a new > > > cgroup. > > > > I'm not 100% sure about the benefit or have a strong opinion one way > > or another, but this sounds like a nice-to-have detail to me, and a relatively > > low cost one (both in effort and at runtime) at that too. > > > > Propagating the change everytime we modify the memory.zswap.writeback > > value of the ancestor might be data race-prone (and costly, depending on > > how big the cgroup subtree is), but this is just a one-time-per-cgroup > > propagation (at the new cgroup creation time). > > I think Yosary was suggesting inheriting the initial value from > parents. That is just one level look up when you create the new > cgroup, using the parent value as default. No recursive. > What you described above seems different to me. I understand what you > are suggesting is that writing to the parent cgroup will recursively > write to all child cgroup. > > > > Can anyone come up with a failure case for this change, or why it might be > > a bad idea? > > I would suggest against recursive changing value behavior. > What if you want the parent but also want the child to keep its value > not changed? Every change to the parent will have to go through the > child to flip it back. > Inherit from the parent seems fine. > > Chris Hi Chris, I've actually sent out a new version of the patch series implementing (what I believed to be) Yosry's suggestion. Feel free to take a look! https://lore.kernel.org/all/20231106231158.380730-1-nphamcs@gmail.com/ Here, I was actually agreeing with you - recursive propagation would not be a good idea. Best, Nhat
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 606b2e0eac4b..18c4171392ea 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1672,6 +1672,17 @@ 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 which exists on non-root + cgroups. The default value is "1". + + 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 522ae22ccb84..b987e58edb70 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 95f6c9e60ed1..e51eafdf2a15 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; @@ -1931,6 +1937,7 @@ 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) { @@ -1944,6 +1951,11 @@ 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 cbd373ba88d2..b4997e27a74b 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_lruvec_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_init(struct lruvec *lruvec) {} static inline void zswap_lruvec_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 e43b5aba8efc..8a6aadcc103c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5545,6 +5545,7 @@ 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, true); #endif page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); if (parent) { @@ -8177,6 +8178,12 @@ 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) { @@ -8209,6 +8216,31 @@ 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", @@ -8221,6 +8253,12 @@ static struct cftype zswap_files[] = { .seq_show = zswap_max_show, .write = zswap_max_write, }, + { + .name = "zswap.writeback", + .flags = CFTYPE_NOT_ON_ROOT, + .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 cab053831fea..e5044678de8b 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 260e01180ee0..051f4487c9ab 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -150,6 +150,11 @@ module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644); static bool zswap_shrinker_enabled; module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644); +bool is_zswap_enabled(void) +{ + return zswap_enabled; +} + /********************************* * data structures **********************************/ @@ -590,6 +595,9 @@ static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, struct zswap_pool *pool = shrinker->private_data; bool encountered_page_in_swapcache = false; + if (!mem_cgroup_zswap_writeback_enabled(sc->memcg)) + return SHRINK_STOP; + nr_protected = atomic_long_read(&lruvec->zswap_lruvec_state.nr_zswap_protected); lru_size = list_lru_shrink_count(&pool->list_lru, sc); @@ -620,6 +628,9 @@ 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 (!mem_cgroup_zswap_writeback_enabled(memcg)) + return 0; + #ifdef CONFIG_MEMCG_KMEM cgroup_rstat_flush(memcg->css.cgroup); nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT; @@ -935,6 +946,9 @@ 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.
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. 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). Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Nhat Pham <nphamcs@gmail.com> --- Documentation/admin-guide/cgroup-v2.rst | 11 +++++++ 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 | 14 +++++++++ 8 files changed, 94 insertions(+), 2 deletions(-)