在 2021/3/3 15:46, Michal Hocko 写道: > On Tue 02-03-21 17:56:07, Johannes Weiner wrote: >> On Tue, Mar 02, 2021 at 12:24:41PM -0800, Hugh Dickins wrote: >>> On Tue, 2 Mar 2021, Michal Hocko wrote: >>>> [Cc Johannes for awareness and fixup Nick's email] >>>> >>>> On Tue 02-03-21 01:34:51, Zhou Guanghui wrote: >>>>> When split page, the memory cgroup info recorded in first page is >>>>> not copied to tail pages. In this case, when the tail pages are >>>>> freed, the uncharge operation is not performed. As a result, the >>>>> usage of this memcg keeps increasing, and the OOM may occur. >>>>> >>>>> So, the copying of first page's memory cgroup info to tail pages >>>>> is needed when split page. >>>> >>>> I was not aware that alloc_pages_exact is used for accounted allocations >>>> but git grep told me otherwise so this is not a theoretical one. Both >>>> users (arm64 and s390 kvm) are quite recent AFAICS. split_page is also >>>> used in dma allocator but I got lost in indirection so I have no idea >>>> whether there are any users there. >>> >>> Yes, it's a bit worrying that such a low-level thing as split_page() >>> can now get caught up in memcg accounting, but I suppose that's okay. >>> >>> I feel rather strongly that whichever way it is done, THP splitting >>> and split_page() should use the same interface to memcg. >>> >>> And a look at mem_cgroup_split_huge_fixup() suggests that nowadays >>> there need to be css_get()s too - or better, a css_get_many(). >>> >>> Its #ifdef CONFIG_TRANSPARENT_HUGEPAGE should be removed, rename >>> it mem_cgroup_split_page_fixup(), and take order from caller. >> >> +1 >> >> There is already a split_page_owner() in both these places as well >> which does a similar thing. Mabye we can match that by calling it >> split_page_memcg() and having it take a nr of pages? > > Sounds good to me. > Hi, Michal, Johannes, Hugh, and Zi Yan, thank you for taking time for this. I agree, and will send v2 patches for taking these. Thanks
