> On May 28, 2023, at 02:54, Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > On Sat, May 27, 2023 at 8:07 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: >> >> On Fri, May 26, 2023 at 09:13:05PM -0700, Yosry Ahmed wrote: >>> On Fri, May 26, 2023 at 9:01 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: >>>> >>>> On Sat, May 27, 2023 at 06:31:26PM +0800, Miaohe Lin wrote: >>>>> The function mem_cgroup_from_obj() is not used anymore. Remove it and >>>>> clean up relevant comments. >>>> >>>> You should have looked at the git history to see why it was created >>>> and who used it. >>>> >>>> Shakeel, Vasily, are you going to retry adding commit 1d0403d20f6c? >>> >>> That commit did not introduce the function though, no? It was >>> introduced before it and replaced by other variants over time (like >>> mem_cgroup_from_slab_obj()). It looks like that commit was reverted ~9 >>> months ago. We can always bring it back if/when needed. >> >> The commit immediately preceding it is fc4db90fe71e. >> >> Of course we can bring it back. It's just code. But avoiding >> unnecessary churn is also good. Let's wait to hear from Vasily. >> >>> It also looks to me that 1d0403d20f6c was using mem_cgroup_from_obj() >>> on a struct net object, which is allocated in net_alloc() from a slab >>> cache, so mem_cgroup_from_slab_obj() should be sufficient, no? >> >> Clearly not. > > I dived deeper into the history on LKML, and you are right: > https://lore.kernel.org/all/Yp4F6n2Ie32re7Ed@qian/ > > I still do not understand why mem_cgroup_from_slab_obj() would not be > sufficient, so I am hoping Vasily or Shakeel can help me understand > here. Seems to be something arch-specific. I think it is because *init_net* which is not allocated from slab meant its address does not belong to linear mapping addresses on arm64. However, virt_to_page() is only applicable to linear mapping addresses. So, mem_cgroup_from_slab_obj() is not sufficient. mem_cgroup_from_obj() is used in this case, which will use vmalloc_to_page() for the page associated with *init_net*. If Vasily does not want to bring commit 1d0403d20f6c back, this patch LGTM. Otherwise, let's wait for Vasily. Thanks.
