On Fri, Sep 17, 2021 at 9:29 AM Roman Gushchin <guro@xxxxxx> wrote: > > Hi Muchun! > > On Thu, Sep 16, 2021 at 09:47:35PM +0800, Muchun Song wrote: > > This version is rebased over linux 5.15-rc1, because Shakeel has asked me > > if I could do that. I rework some code suggested by Roman as well in this > > version. I have not removed the Acked-by tags which are from Roman, because > > this version is not based on the folio relevant. If Roman wants me to > > do this, please let me know, thanks. > > I'm fine with this, thanks for clarifying. > > > > > Since the following patchsets applied. All the kernel memory are charged > > with the new APIs of obj_cgroup. > > > > [v17,00/19] The new cgroup slab memory controller[1] > > [v5,0/7] Use obj_cgroup APIs to charge kmem pages[2] > > > > But user memory allocations (LRU pages) pinning memcgs for a long time - > > it exists at a larger scale and is causing recurring problems in the real > > world: page cache doesn't get reclaimed for a long time, or is used by the > > second, third, fourth, ... instance of the same job that was restarted into > > a new cgroup every time. Unreclaimable dying cgroups pile up, waste memory, > > and make page reclaim very inefficient. > > I've an idea: what if we use struct list_lru_memcg as an intermediate object > between an individual page and struct mem_cgroup? > > It could contain a pointer to a memory cgroup structure (not even sure if a > reference is needed), and a lru page can contain a pointer to the lruvec instead > of memcg/objcg. Hi Roman, If I understand properly, here you mean the struct page has a pointer to the struct lruvec not struct list_lru_memcg. What's the functionality of the struct list_lru_memcg? Would you mind exposing more details? > > This approach can probably simplify the locking scheme. But what's more > important, it can dramatically reduce the number of css_get()/put() calls. > The latter are not particularly cheap after the deletion of a cgroup: > they are atomic_dec()'s. As a result, the reclaim efficiency could be much > better. The downside: we will need to update page->lruvec_memcg pointers on > reparenting pages during the cgroup removal. Here we need to update page->lruvec_memcg pointers one by one, right? Because the lru lock is per lruvec, the locking scheme still need to be as proposed by this series when the page->lruvec_memcg is changed If I understand properly. It's likely that I don't get your point. Looking forward to your further details. Thanks. > > This is a rough idea, maybe there are significant reasons why it's not possible > or will be way worse. But I think it's worth discussing. What do you think? > > Thanks!
