On 2/15/24 19:29, Kent Overstreet wrote:

On Thu, Feb 15, 2024 at 08:47:59AM -0800, Suren Baghdasaryan wrote:

quoted

On Thu, Feb 15, 2024 at 8:45 AM Michal Hocko [off-list ref] wrote:

quoted

On Thu 15-02-24 06:58:42, Suren Baghdasaryan wrote:

quoted

On Thu, Feb 15, 2024 at 1:22 AM Michal Hocko [off-list ref] wrote:

quoted

On Mon 12-02-24 13:39:17, Suren Baghdasaryan wrote:
[...]

quoted

@@ -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?