| Message ID | 20190717202413.13237-3-longman@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm, slab: Extend slab/shrink to shrink all memcg caches | expand |
On Wed, 17 Jul 2019, Waiman Long wrote: > The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently > returns nothing. This is now modified to show the time of the last > cache shrink operation in us. What is this useful for? Any use cases? > CONFIG_SLUB_DEBUG depends on CONFIG_SYSFS. So the new shrink_us field > is always available to the shrink methods. Aside from minimal systems without CONFIG_SYSFS... Does this build without CONFIG_SYSFS?
On 7/18/19 7:39 AM, Christopher Lameter wrote: > On Wed, 17 Jul 2019, Waiman Long wrote: > >> The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently >> returns nothing. This is now modified to show the time of the last >> cache shrink operation in us. > What is this useful for? Any use cases? I got query about how much time will the slab_mutex be held when shrinking the cache. I don't have a solid answer as it depends on how many memcg caches are there. This patch is a partial answer to that as it give a rough upper bound of the lock hold time. >> CONFIG_SLUB_DEBUG depends on CONFIG_SYSFS. So the new shrink_us field >> is always available to the shrink methods. > Aside from minimal systems without CONFIG_SYSFS... Does this build without > CONFIG_SYSFS? The sysfs code in mm/slub.c is guarded by CONFIG_SLUB_DEBUG which, in turn, depends on CONFIG_SYSFS. So if CONFIG_SYSFS is off, the shrink sysfs methods will be off as well. I haven't tried doing a minimal build. I will certainly try that, but I don't expect any problem here. Cheers, Longman
On 7/18/19 10:36 AM, Waiman Long wrote: >>> CONFIG_SLUB_DEBUG depends on CONFIG_SYSFS. So the new shrink_us field >>> is always available to the shrink methods. >> Aside from minimal systems without CONFIG_SYSFS... Does this build without >> CONFIG_SYSFS? > The sysfs code in mm/slub.c is guarded by CONFIG_SLUB_DEBUG which, in > turn, depends on CONFIG_SYSFS. So if CONFIG_SYSFS is off, the shrink > sysfs methods will be off as well. I haven't tried doing a minimal > build. I will certainly try that, but I don't expect any problem here. I have tried a tiny config with slub. There was no compilation problem. -Longman
On Wed 17-07-19 16:24:13, Waiman Long wrote: > The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently > returns nothing. This is now modified to show the time of the last > cache shrink operation in us. Isn't this something that tracing can be used for without any kernel modifications?
On 7/19/19 2:14 AM, Michal Hocko wrote: > On Wed 17-07-19 16:24:13, Waiman Long wrote: >> The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently >> returns nothing. This is now modified to show the time of the last >> cache shrink operation in us. > Isn't this something that tracing can be used for without any kernel > modifications? That is true, but it will be a bit more cumbersome to get the data. Anyway, this is just a nice to have patch for me. I am perfectly fine with dropping it if this does not prove to be that useful. Thanks, Longman
On Fri 19-07-19 10:07:20, Waiman Long wrote: > On 7/19/19 2:14 AM, Michal Hocko wrote: > > On Wed 17-07-19 16:24:13, Waiman Long wrote: > >> The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently > >> returns nothing. This is now modified to show the time of the last > >> cache shrink operation in us. > > Isn't this something that tracing can be used for without any kernel > > modifications? > > That is true, but it will be a bit more cumbersome to get the data. I have no say for this code but if there is a way to capture timing data I prefer to rely on the tracing infrastructure. If the current tooling makes it cumbersome to get then this is a good reason to ask for a less cumbersome way. On the other hand, if you somehow hardwire it to a user visible interface then you just establish ABI which might stand in way for potential/future development. So take it as my 2c
diff --git a/Documentation/ABI/testing/sysfs-kernel-slab b/Documentation/ABI/testing/sysfs-kernel-slab index 94ffd47fc8d7..9869a3f57dc3 100644 --- a/Documentation/ABI/testing/sysfs-kernel-slab +++ b/Documentation/ABI/testing/sysfs-kernel-slab @@ -437,6 +437,8 @@ Description: write for shrinking the cache. Other input values are considered invalid. If it is a root cache, all the child memcg caches will also be shrunk, if available. + When read, the time in us of the last cache shrink + operation is shown. What: /sys/kernel/slab/cache/slab_size Date: May 2007 diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h index d2153789bd9f..055474197e83 100644 --- a/include/linux/slub_def.h +++ b/include/linux/slub_def.h @@ -113,6 +113,7 @@ struct kmem_cache { /* For propagation, maximum size of a stored attr */ unsigned int max_attr_size; #ifdef CONFIG_SYSFS + unsigned int shrink_us; /* Cache shrink time in us */ struct kset *memcg_kset; #endif #endif diff --git a/mm/slub.c b/mm/slub.c index 9736eb10dcb8..77d67a55ce43 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -34,6 +34,7 @@ #include <linux/prefetch.h> #include <linux/memcontrol.h> #include <linux/random.h> +#include <linux/sched/clock.h> #include <trace/events/kmem.h> @@ -5287,16 +5288,21 @@ SLAB_ATTR(failslab); static ssize_t shrink_show(struct kmem_cache *s, char *buf) { - return 0; + return sprintf(buf, "%u\n", s->shrink_us); } static ssize_t shrink_store(struct kmem_cache *s, const char *buf, size_t length) { - if (buf[0] == '1') + if (buf[0] == '1') { + u64 start = sched_clock(); + kmem_cache_shrink_all(s); - else + s->shrink_us = (unsigned int)div_u64(sched_clock() - start, + NSEC_PER_USEC); + } else { return -EINVAL; + } return length; } SLAB_ATTR(shrink);
The show method of /sys/kernel/slab/<slab>/shrink sysfs file currently returns nothing. This is now modified to show the time of the last cache shrink operation in us. CONFIG_SLUB_DEBUG depends on CONFIG_SYSFS. So the new shrink_us field is always available to the shrink methods. Signed-off-by: Waiman Long <longman@redhat.com> --- Documentation/ABI/testing/sysfs-kernel-slab | 2 ++ include/linux/slub_def.h | 1 + mm/slub.c | 12 +++++++++--- 3 files changed, 12 insertions(+), 3 deletions(-)