On Fri, Sep 6, 2024 at 10:29 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > On 9/6/24 19:19, Yosry Ahmed wrote: > > [..] > >> I felt it could be improved more, so ended up with this. Thoughts? > >> > >> /** > >> * kmem_cache_charge - memcg charge an already allocated slab memory > >> * @objp: address of the slab object to memcg charge > >> * @gfpflags: describe the allocation context > >> * > >> * kmem_cache_charge allows charging a slab object to the current memcg, > >> * primarily in cases where charging at allocation time might not be possible > >> * because the target memcg is not known (i.e. softirq context) > >> * > >> * The objp should be pointer returned by the slab allocator functions like > >> * kmalloc (with __GFP_ACCOUNT in flags) or kmem_cache_alloc. The memcg charge > > > > Aren't allocations done with kmalloc(__GFP_ACCOUNT) already accounted? > > Why would we need to call kmem_cache_charge() for those? > > AFAIU current_obj_cgroup() returns NULL because we're in the interrupt > context and no remote memcg context has been set. Thus the charging is > skipped. The patch commit log describes such scenario for network receive. Oh yeah I missed that part. I thought the networking allocations in interrupt context are made without __GFP_ACCOUNT to begin with. > But in case of kmalloc() the allocation must have been still attempted with > __GFP_ACCOUNT so a kmalloc-cg cache is used even if the charging fails. It is still possible that the initial allocation did not have __GFP_ACCOUNT, but not from a KMALLOC_NORMAL cache (e.g. KMALLOC_DMA or KMALLOC_RECLAIM). In this case kmem_cache_charge() should still work, right? > > If there's another usage for kmem_cache_charge() where the memcg is > available but we don't want to charge immediately on purpose (such as the > Linus' idea for struct file), we might need to find another way to tell > kmalloc() to use the kmalloc-cg cache but not charge immediately... Can we just use a dedicated kmem_cache for this instead?
