On Thu, Feb 15, 2024 at 09:22:07PM +0100, Vlastimil Babka wrote: > On 2/15/24 19:29, Kent Overstreet wrote: > > On Thu, Feb 15, 2024 at 08:47:59AM -0800, Suren Baghdasaryan wrote: > >> On Thu, Feb 15, 2024 at 8:45 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > >> > > >> > On Thu 15-02-24 06:58:42, Suren Baghdasaryan wrote: > >> > > On Thu, Feb 15, 2024 at 1:22 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > >> > > > > >> > > > On Mon 12-02-24 13:39:17, Suren Baghdasaryan wrote: > >> > > > [...] > >> > > > > @@ -423,4 +424,18 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) > >> > > > > #ifdef CONFIG_MEMORY_FAILURE > >> > > > > printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages)); > >> > > > > #endif > >> > > > > +#ifdef CONFIG_MEM_ALLOC_PROFILING > >> > > > > + { > >> > > > > + struct seq_buf s; > >> > > > > + char *buf = kmalloc(4096, GFP_ATOMIC); > >> > > > > + > >> > > > > + if (buf) { > >> > > > > + printk("Memory allocations:\n"); > >> > > > > + seq_buf_init(&s, buf, 4096); > >> > > > > + alloc_tags_show_mem_report(&s); > >> > > > > + printk("%s", buf); > >> > > > > + kfree(buf); > >> > > > > + } > >> > > > > + } > >> > > > > +#endif > >> > > > > >> > > > I am pretty sure I have already objected to this. Memory allocations in > >> > > > the oom path are simply no go unless there is absolutely no other way > >> > > > around that. In this case the buffer could be preallocated. > >> > > > >> > > Good point. We will change this to a smaller buffer allocated on the > >> > > stack and will print records one-by-one. Thanks! > >> > > >> > __show_mem could be called with a very deep call chains. A single > >> > pre-allocated buffer should just do ok. > >> > >> Ack. Will do. > > > > No, we're not going to permanently burn 4k here. > > > > It's completely fine if the allocation fails, there's nothing "unsafe" > > about doing a GFP_ATOMIC allocation here. > > Well, I think without __GFP_NOWARN it will cause a warning and thus > recursion into __show_mem(), potentially infinite? Which is of course > trivial to fix, but I'd myself rather sacrifice a bit of memory to get this > potentially very useful output, if I enabled the profiling. The necessary > memory overhead of page_ext and slabobj_ext makes the printing buffer > overhead negligible in comparison? __GFP_NOWARN is a good point, we should have that. But - and correct me if I'm wrong here - doesn't an OOM kick in well before GFP_ATOMIC 4k allocations are failing? I'd expect the system to be well and truly hosed at that point. If we want this report to be 100% reliable, then yes the preallocated buffer makes sense - but I don't think 100% makes sense here; I think we can accept ~99% and give back that 4k.