On 2021/4/6 19:39, Michal Hocko wrote:
On Tue 06-04-21 19:30:22, Neil Sun wrote:
On 2021/4/6 15:21, Michal Hocko wrote:
You are changing semantic of the existing user interface. This knob has
never been memcg aware and it is supposed to have a global impact. I do
not think we can simply change that without some users being surprised
or even breaking them.
Yes, do you think add new interface to sysfs is a good way? such as
/sys/fs/cgroup/memory/lxc/i-vbe1u8o7/memory.kmem.drop_caches
There were other attempts to add a memcg specific alternative to
drop_caches. A lack of a strong usecase has been a reason that no such
attempt has been merged until now. drop_caches is a problematic
interface because it is really coarse and people have learned to (ab)use
it to workaround problem rather than fix them properly.
What is your usecase?
We have some lxc containers running on the server, when mysqld running
backup jobs in the container, page cache will grow up and eat up all
unused memory in the container, then some new jobs come, we can see that
tasks are busy on allocing memory with reclaiming, so we want to drop
page cache after mysql backup job for individual container, it will
speed up allocing memory when new jobs come.
This patch only drop slab cache but not page cache, this can be the
first step if people really need this interface.
---
Neil
