Re: [PATCH] mm/util.c: Added page count to __vm_enough_memory failure warning

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On 21.02.24 17:02, Matthew Cassell wrote:
Commit 44b414c8715c5dcf53288 ("mm/util.c: add warning if __vm_enough_memory
fails") adds debug information which gives the process id and executable name
should __vm_enough_memory() fail. Adding the number of pages to the failure
message would benefit application developers and system administrators in
debugging overambitious memory requests by providing a point of reference to
the amount of memory causing __vm_enough_memory() to fail.

1. Set appropriate kernel tunable to reach code path for failure
    message:

	# echo 2 > /proc/sys/vm/overcommit_memory

2. Test program to generate failure - requests 1 gibibyte per iteration:

	#include <stdlib.h>
	#include <stdio.h>

	int main(int argc, char **argv) {
		for(;;) {
			if(malloc(1<<30) == NULL)
				break;

			printf("allocated 1 GiB\n");
		}

		return 0;
	}

3. Output:

	Before:

	__vm_enough_memory: pid: 1218, comm: a.out, not enough
memory for the allocation

	After:

	__vm_enough_memory: pid: 1141, comm: a.out, pages: 262145, not
enough memory for the allocation

Signed-off-by: Matthew Cassell <mcassell411@xxxxxxxxx>
---
  mm/util.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 5a6a9802583b..c0afb56f16ea 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -976,8 +976,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
  	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
  		return 0;
  error:
-	pr_warn_ratelimited("%s: pid: %d, comm: %s, not enough memory for the allocation\n",
-			    __func__, current->pid, current->comm);
+	pr_warn_ratelimited("%s: pid: %d, comm: %s, pages: %ld, not enough memory for the allocation\n",
+			    __func__, current->pid, current->comm, pages);
  	vm_unacct_memory(pages);
return -ENOMEM;

I wonder if "bytes"/"kbytes" instead of pages would be more appropriate here.

Often, this will fail due to mmap() [where we pass a size from user space] and also "vm.overcommit_kbytes" is not in pages.

--
Cheers,

David / dhildenb





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