linux-kernel - [PATCH v2] mm/util.c: Added byte count to __vm_enough

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Message-Id: <20240222194617.1255-1-mcassell411@gmail.com>
Date: Thu, 22 Feb 2024 19:46:17 +0000
From: Matthew Cassell <mcassell411@...il.com>
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	david@...hat.com,
	mcassell411@...il.com
Subject: [PATCH v2] mm/util.c: Added byte count to __vm_enough_memory failure warning

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: 1137, comm: a.out, bytes: 1073741824,
not enough memory for the allocation

Signed-off-by: Matthew Cassell <mcassell411@...il.com>
---
Changed the debug output from the number of pages to the number of
bytes.
 mm/util.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 5a6a9802583b..6710efaf1802 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -942,6 +942,7 @@ EXPORT_SYMBOL_GPL(vm_memory_committed);
 int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 {
 	long allowed;
+	unsigned long bytes_failed;
 
 	vm_acct_memory(pages);
 
@@ -976,8 +977,9 @@ 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);
+	bytes_failed = pages << PAGE_SHIFT;
+	pr_warn_ratelimited("%s: pid: %d, comm: %s, bytes: %lu not enough memory for the allocation\n",
+			    __func__, current->pid, current->comm, bytes_failed);
 	vm_unacct_memory(pages);
 
 	return -ENOMEM;
-- 
2.43.2